That’s not good Vinnie, have you started a formal complaint with motability? May sound a bit extreme, but your car has bluetooth as a standard feature of the car, so if it’s not working correctly it needs to be fixed – regardless if the garage is unable to replicate the fault themselves, they should take your word, and as you say, a replacement unit would seem the 1st economical port of call – cheap part and easily swapped in/out.