1997 Volkswagen Polo Took Car Service Change Break Pads Ball Joints Days Later

i took my car for service to change break pads, ball joints and a few days later the car stopped when driving. a mechanic told me the ignition coil had failed and i have replaced it but the car wont start since the battery was low. upon trying to jumpstart the car the vehicle engine blew up. what may have caused this and how can i fix it since the car cannot start. p.s the ignition coil is still working