Something similar happened to me a few years back but it was for my car. The manager(Not the owner) of the garage gave me a discount of 300 euro as he did business with my missus. The work on the car was coming to 1800e as needed quite a bit of work, so paid 1500 euro, happy days, but I got a phone call from the actual owner the following Monday saying I had to pay the 300 euro, and that the manager had no business giving me a discount which is fair enough, but he did, so not my probleam, he got very agressive and rude, and this went for a few weeks, to cut a long short short I told him to get lost and didn't pay him, your story is pretty much the same as mine.