Good luck getting the refund. In future, you could cancel the DD and ask them for a final bill which you will pay by cheque or bank transfer. Just record your letter/email and save it in case of future problems. If you ever get a debt collection company calling, you will have all your evidence to show them, then say any further calls by them will be considered harassment and you will call the police.

So, yes, you're thinking you might have hassle in the future, but you've just had a month or so of hassle dealing with a company who wont communicate with you and which has access to your bank funds.....and they aren't alone in this type of behaviour.