How to write a letter to a bank for withdrawing the funds from the blocked account?

My bank account in one of the UK bank`s has been closed. And they keep my money and closed my account as well, because i am not UK student any more and the account was not active for past 2 months. How can i write a letter to bank to transfer my money to my USA account?i would appreciate if anybody could give me a sample letter as well. Thank you in advance.