Billing of Cell phone Insurance that was cancelled

I went into Foschini Canal Walk to cancel the cell phone insurance on my account and was told that I cant do it in store I must call in. I called in to cancel both cell phone insurance that was on my account December 2014 or January 2015 not sure which month. I have also skipped payments for more then 3 months and the insurance was cancelled from their side due to non payment. My account was paid up in full only to receive a statement which i was billed for two cell phone insurance that i cancelled months ago. i called in to query and was told they have to run back on all their calls which is November 2014. This is unacceptable and i want Foschini to credit me as I refuse to pay for something that I cancelled months ago. Their service is pathetic...