Contact cut as ex moving away & childs behaviour

Please can anyone help me prepare for the storm ahead that I just know is coming - once our divorce has finally been sorted after nearly two years, and my ex has got what she wanted and most of my money I know she'll start on about the CM issue that is brewing, and I really need to know where I stand.

I am the NRP. Originally CM was set via mediation at £30pw, cash paid privately per week. The contact arrangement was that I would have my son every wednesday night and every other weekend from Sat morning to Sun eve. Some time later my stbx decided that £30pw was not enough,and involved csa albeit on a private basis. In the meantime my partner and her child moved in with me, which then chopped stbx's csa-guided CM down to £26pw. Much howling from stbx as she obviously thought she was entitled to more.

Anyway, since Feb 09-present my son has delevoped an extreme behaviour problem which involves amongst other things screaming to go home to mummy every single overnight stay. I tried to cope with this but it became too much for all involved and eventually had to curtail the Weds night stays, these turned into tea-visits instead - he's 4 and just starting school so weekday overnighters would have had to have stopped anyway. Then my stbx started playing up via abusive texts & letters from csa - more CM was demanded due to the dropping of the weds night - i.e. my stbx was putting CM before the welfare and happiness of her child, because he hated staying overnight here. I managed to fight this and things went quiet after a fashion.

Since then the behaviour, which was denied as being a problem by my stbx, started to come out at school, and then in front of my ex mother in law, when he kicked my stbx in front of her. A referral was made via the doctors, adhd diagnosed, he has had a few visits to a counsellor, so finally some kind of headway is being made there. Then the behaviour escalated even more and turned the Saturday night visit into a war zone - he wanted to go home, screaming, kicking and swearing at me. Eventually after much arguing stbx agreed that he could be taken home on a Saturday night and picked up the following morning. This plan worked - needless to say my ex took the credit for 'her' plan of making our son happy!!! Anyway, I bet you're thinking now here comes yet another csa letter for more money, as I was...however, nothing has happened and she has continued to accept the original £26pw.

BUT in the last few weeks she has announced to me that she, my son and her new partner are 'moving away to make a fresh start', approximately 30 miles away. Because DS is unhappy to stay overnight, this knocks down my contact to every other Sunday, which obviously I and my family are very unhappy about, although clearly there is not a lot I can do about it. We have agreed to alternate pick ups and drop offs. Of course I am now waiting for the bombshell letter from the csa telling me that I owe arrears on when the overnighters stopped - my main question is can she actually do this given that we now have medical advice that he is adhd, that he needs counselling and so this is why I had to stop them, AND that the main reason my contact has been chopped so much is because of her moving? In the csa guidebook it really isn't clear.

Sorry for the long story but I wanted to give a full back-ground picture, many thanks.

Firstly, never EVER pay CM in cash, whether its private or CSA agreed. And if you have no choice, ensure she gives you a 'reciept' each time.

When my OH and his ex first split he paid her a lump sump every month for informal CM and SM.
A few months after I came on the scene we got to digging around in finances this changed to 2 standing orders, one named SM the other named CM just in case she ever came back and claimed via the CSA she could have argued the lump sum was ONLY for bills etc;

Right, secondly.
Its quite unfair about the move, however if the behaviour improves is there any chance of overnights being introduced again? Maybe even a trial basis? Ableit slowly I am sure.
Children cope and chop and change very easily..now that he is going to start school and home isn't his entire life anymore he may settle down. 30 miles is about 45 mins each way so not entirely out of the question.
I would put the CM issue to one side for the momemnt, continue to pay what you do and concentrate on building up the contact again maybe over a 6 month scale, then keep it going for another 6 months until broaching the subject of CM. Especially given it was not you doing the relocating.
Then worry about the CM. If she then buggers around with the contact after a routine has been established as a clear attempt at getting more CM then it should be clear that is the motive.
You are also at liberty to contact the CSA at any point yourself for an assessment even as the NRP. Also worth noting that the CSA will take into account the cost of travelling to collect/drop off if this exceeds a certain percentage of the weekly payment. So even if you picked up and dropped off every week the CM may stay as it is as they may take into account petrol/train costs.
Hope that helps a bit, its most important to keep the contact and the overnight stays the main priority for the minute and worry about the CSA/CM later on.