Bad service

I jave been using rain Simcard for almost 2years now, the thing is I moved to a location where it doesnt cover very well last 3 months, I only missed 2 payments of which they stopped the data connection I thought I was owing R500 which is for 2 months but I cancelled the sim but they billed me for last month and even counting a debit order for this month even when I cancelled the sim a months back, how can I solve this issue because their customer service is bad they will just send you the same invoice showing how much uou owe instead of solving our issues?

They still charge me when I cancelled the sim thats unbelievable I cant pay 950 for 2 months data I did not use since cancellation