By debit card... if only I’d used a credible card

Does anyone have experience of getting their deposit back from these people? They took a deposit, but messed me about saying they hadn’t got the paperwork, making it almost impossible to sort out the road tax. Had me running backs and forwards trying different things to sort out paperwork at post office but obviously they would not accept my application for tax. Explained to Harley Wintney Motors the situation and they said no, can’t have deposit. Mysteriously they reckoned then to have paper after all. Then they fibbed about mot advisory work having been done, which haddock been looked out. Eventually they said they had given my deposit back, but they did not. Anyone have any ideas?