1) If they're not responding to you, it's possible they've written you off. It's possible they put the unit back up for sale instead of even starting the repairs and waiting to see if you ever come back for your deposit. By not returning calls, they can stall having you ask for your deposit back.
2) Regarding the BBB, they don't always fix the problems. Years ago I ran into an issue with my phone company. I cancelled my phone line when I sold my house. They cancelled the account, but continued to send me a monthly bill and expected me to continue paying for services not rendered. I tried to file a BBB complaint but the BBB came back saying they were a hopeless case, they couldn't get them to do anything, and sorry about your luck. (Note: the issue finally went away, but it took like 1.5 years to straighten out. In the end I ended up paying for equipment not returned (which they never came to get) and they wiped out the service charges.)
There's no use crying over spilled milk, unless it's on your keyboard.