Age limit for child care tax credits

Is there an age limit for receiving child care tax credits.HMRC stopped my payments. The 2011/12 award says that there are no qualifying child care costs. When I call them they simply refuse to discuss it.
I have now lodged a complaint with the tax Adjudicator because I am getting no where with HMRC.
I just want to check at what age it is considered unreasonable to pay child care tax credits?

They stopped my son's automatically when he turned 16 but if you talk to them they do keep paying it until he's 19 because he's in full time education.

The wording from their renewal document notes is "A young person is in full time education if they started, accepted or enrolled on their current course before age 19". Then goes on to describe what they consider full time education. Basically its if they are in school or college doing subjects up to A level or NVQ level 3 but not uni degrees. They must be in lessons for more than 12 hours a week.

Hope that helps a bit.

P.S. I don't have child care costs so this is for the child element of working tax credits.

It isn't the child element, I get that. It is the child care that they wont pay. They refuse to give a reason why they wont pay it.
The child is now 12 and it going to secondary school so the chld care stopped in September but they stopped paying a few months back.
I am owed about £1400. Bearing in mind I don't get CM at all this is a huge loss.