Cell C does not want to repair my phone

Purchased an Iphone with Cell C May 2014. in March 2015 (after the last version upgrade) my phone started freezing and eventually I couldn't do anything on the phone. I sent the phone in on 30 March 2015, Cell C responded a month later saying I have to pay R6000 for repairs, my phone was sent well in time for it to be repaired under warranty. I contacted my insurance and they said they do not repair phones that have faulty software, therefore they will not pay out. Till today I have not had constructive feedback. I have notified Cell C that I would like to cancel my contract and still no constructive response. I pay my cell phone contract every month will no issues, this has caused a major inconvenience for me and my family. I had been with MTN for many years before changing to Cell C and I regret switching networks because I never had an issue with them.