Complaint of service negligence at Renault Benoni

Renault Benoni is the worst Renault dealer i have ever come across. At 90000km my car was not serviced properly. The timing and accessories belts were not replaced. Now a year later my car' s engine is failing and they are refusing to fix it. I laid a complaint via email with Renault SA there is response. I tried calling their customer care my calls are being cut. Im really frustrated. Please help