hi
all communication to them needs to be in writing and sent certified mail with return receipt requested - in the letter demand the refund for their breach of contract as discussed on whatever date -explain that if you do not get the money within 10 days from the receipt of the letter, you will have no other option but to file a civil lawsuit, where you will claim the deposit, interest you have lost by not having the money in your bank and any and all filing fees associated with the suit.
keep a copy of the letter and when you get the receipt back from the post office - if they dont respond in the 10 day time period you will need to file a lawsuit. small claims is easy to handle on your own.
Attorney at Law
20 years practicing law