Very poor service delivery from management

Took my car for a service and explained to the lady that there was a noise in the motor at cold start up. When I collected the cat she said that they put some engine flush in and that it's ok now. But must phone if the car does the same. So the next morning it did the same thing. Called them up on the 12th of February to explain again. Where she told me the manager is out of the office but they will call me back. Nothing untill I phoned again on the 22nd of February spoke to the manager where he said he will call me back but nothing from them. Who can assist me with this problem. Who can I contact with this issue.