Shocking repair service and incorrect diagnoses

I handed in my iPhone 6 for repairs on the 17/08/2015. This phone was replaced under insurance a month before. I had to pay a shocking 20% co-payment something I wasnt told when I signed up through vodacom insurance. 4 Weeks later the earpiece speaker stopped working and I could only receive calls on speaker phone. I handed the phone in as it's still under warranty from the manufacturer. I had to phone vodacom 4 times before I was told that my phone had liquid damage and I need to cover the repair cost. This is absolute nonsense and an easy way for them to not honor their warranty. How do I proof the phone did not suffer liquid damage? I paid R2800 1 month ago for a phone that they don't want to repair and I pay R250 per month just for insurance. If I can advise anyone do not buy an iPhone and do not take vodacom insurance. This is an absolute racket.