Business assurances for refunfable deposits are useless - they are in business to make money. What you need to do is find out if this is stated in writing anywhere. If it does, and you have adhered to your part, you have the right to your money back as per the contractual agreement. Check the company out on the net to find out a bit more about them first - make sure they are not rogues.
If you can't find anuthing about the deposit return in writing, be nice - you're in their hands now. If what you find in writing is negative, i.e. it says that you are not entitled to a return, you have two options , which are quite lengthy and you will need a solicitor for - 1) Incitment into procurement of a contract, and 2) Unfair contract terms - they are both self explanitory in their meaning, but not for the layperson to put into action.
Good luck