SMR Autoworks unresponsive after paid

SMR Autorks George - (Simion/Lara/Billy) was asked to repair my Opel Vivaro Van due to a misfiring cylinder. Initially very good and fast to respond, quick to ask for money upfront for repairs(which was paid over every time). After 2 weeks the problem happened again and it took them 2 weeks to finally come to fetch the car for further inspection and now another 3 weeks later it is almost impossible to reach them on any number. I have been past the workshop a couple of times with only 1 mechanic there and no sign of the rest. It has been impossible to get a deadline date for my car and still no contact from them.