Mtn don't want to refund my money

I cancelled my contract phone January because my contract was finished, same day I canceled my insurance, February March and April insurance deduct my money. I call Mtn to find out whats going on, I was told to get my money back I have to send my bank statement which I did, the following day they said I must send my invoice which I did, I did attach my invoice more than 3 times, they only reply by saying send your invoice, it shows that they don't take customer serious, I send them many times but they keep on saying send invoice, I'm soo disappointed, I regret why I ever used Mtn.