Unacceptable behaviour from cell c repair center.

Good day I have a problem with cell c repair center regarding my contract phone.It is a Samsung Grand prime and the phone is still under warrenty. The phone just stopped to charge and I took I to waterfall mall cell c for help,they examined my phone and my phone was still on and working,just not charging. They booked my phone for repairs and after a week therepair call center phoned me with a quotation of R1800 claiming there ar liquid damage. I know for a fact it is not the case and liquid damage is unrepairable. I worked as technician at a cell phone repair center and I know they are taking me for granted.I asked the operator to send my phone back and i will follow procedures to proof that it is not the case.I wanted to mail higher management but THE MAIL ADDRESS WATERFALL MALL PROVIDED ME IS PROTECTED BY A MAIL BLOCKER.Please help me to resolve my problem.