Please Help!!

Course and Beacham in Shirley Southampton Hampshire were appointed by my dealership i bought the car from to repair a couple of faults the car had recently came up after I bought it, once I got the car back my dealership paid C&B, but as I drove the car out of the forecourt of the garage the faults were still evident so Geoff at C&B told me to leave the car with him and he'd sort them, When he later called saying the dealership I bought the car from wasn't going to pay him again for the repairs seeming as they already did! and he wouldn't do anything to the car until I call him and pay him the money!

I then contacted my dealership I bought the car from who said they would pick the car up in the morning and sort the repairs from another repairer.

Then Geoff from C&B called me to say hes repaired the car and he wants his £400, I told him the Dealership are picking it up in the morning, to which he then said said hes going to strip the car down to an unroadworthy state until I pay him!

Is there anything I can do?? Please help!