Bad Service and Potential Vehicle Damage

I started experiencing problems with overheating in my car so I decided to take it to Car Service City Germiston for repairs. They repaired the issue successfully but then they later suggested because of the car's poor takeoff after service, they do a major Service on the car, which I authorized. A month of 2 down the line and still within my guarantee with them the car started having an oil leak and smoke everything I drove the car. I then took the car to a mechanic and what was discovered appalled me and left me disappointed. The housing for the oil filter, had ot been tightened after service and additionally, the oil filter had not been changed as it was supposed to during a major service. Furthermore we discovered that the engine oil had not been changed during service, further adding to the car's problems. The only thing changed by Car Service City was the air filter. All of this for R2 517,53(Major Service Quote as Per Car Service City Germiston). This is very disappointing as I had always re**** on them in the past to Service my vehicle... I will be further taking this to the ombudsman for further investigation.