Secure Drive Accounts Dept can't get it right!

Schocking from begining to now. I agreed to a debit order and every month they debit my bank accout yet EVERY month they start harrasing me saying Im in arreas when Im not. It starts with sms's then calls and they are rude to me demanding payment or proof of payment and EVERY month I send proof of payment. It is schocking how their account department can't get it right! I threatened to cancel my contract cause it is seriously not acceptible to be harrasing me and fighing with me for no reason and then they said I must pay R1800 if I want to cancel. It is not about the device or their service or the money, It's about a paying customer being treated so badly for no apparent reason. And every month they say it's sorted till the next month ! I will be writing to the ombudsman about this if you refuse to cancel this contract and continue to demand money for cancelling a contract due to over 2 years of abuse from your Fadelity Secure Drive.