Is CM collected in Arrears or in Advance?

Hey peeps

Just a quick question
i dropped my csa down in july to what the calculator suggested..lo an behold wrath from the ex and a CSA assessment followed. I have to pay £10 more a month than what I dropped it to but £175! Less than what I was (on top of all the marital debt, while she continues to make income from both the FMH and a rental property) plus make what I do in benefits each month)
anyway, I got a letter notifying me that they aren’t collecting any payments from me until the end of September, but I haven’t paid her since august 1st? the payment for end of September includes the arrears from july/august (£20) but what I don’t understand is, is CM collected in arrears? IE do I pay for September at the end of September, and so on and so forth. Effectively my ex will go nearly 9 weeks without any CM. I have no problem paying her direct if this isn’t the case but I cant get sense out of the CSA when I just called, one advisor said to pay her direct, one said to wait till the DD is collected?
I do not have an issue providing for my children but I don’t want her getting anything extra out of me for shoes clothes nights out with her bf when I am struggling to pay my own bills at the minute.

Yes it's collected in arrears, so they're letting you go to the end of September before starting the payment schedule.

thanks chez, just checking before i get a crap text of the MIL asking where it is and that i have fecked her out of a month of CM.
so long as i know i pay her in arrears and not in advance i can just refer her back to them if she has any problems.
i was quite happy to keep the csa out of it if she was willing to discuss it rationally and without screeching at me and using the kids as a quilt trip! oh well frees up more money for them, i got them new shoes on the weekend and sent them home with them..know ill never see them again but i would rather i contributed directly to them than fund her 10 night a month cinema habit.