My collage sent me letter saying i have to pay money after i withdrow from the course?

i was in this collage to study a foundation psychology course. the course was �4000 and i payed half when i started the course. i was very unhappy with the course and by the way how they teach. many studnt withdrow from this course for this reason including me. the course was very disorganised,and they didnt even know when the course is gone finish when we asked the head of the collage. for this reason i withdrow by thinking i have not learnt any thing and it s not worth it to pay that much money. now they sent me a letter saying that i have to pay �2000.i have not recived any contract when i stareted the course and the collage would send a debt collect for legal action with this notice. i wanted to send them a letter but i really wanted to be really good. can any one give me advise and help me writ me a letter as for me english is my second languge and there is always an error when i writ.