WHEN MY DEALER WAS RESETTING THE REGENERATION SYSTEM ON MY CAR THEIR SYSTEM FAILED HALFWAY THROUGH.FOR SOME REASON THEY SAY THEY HAD TO START THE CAR BEFORE RESTARTING THE REGENERATION AGAIN ON DOING THIS THERE WAS A KNOCKING COMING FROM THE ENGINE AND LOSS OF PAS.THEY ARE NOW SAYING THAT ITS NOT THEIR FAULT .BUT AS THE CAR WAS OK UNTIL THEY FIRST SERVICED IT 18 MILES AGO SURELY THIS HAS TO BE SOMETHING THEY HAVE DONE WRONG. IT WENT TO THEM 18 MILES AGO TO GET THE DPF LIGHT PUT OUT NOW IT CANT BE DRIVEN .ANY IDEAS?