MTN Keeps billing for an over a year long cancelled month to month contract!

The MTN Branch and MTN HQ don't seem to communicate yet they are a communications company. I cancelled my 5G LTE ZTE last year March to go on their Supersonic Fiber uncapped. I even filled the return and cancelation forms and brought back their 5G router last year and still they never cancelled and billed me ever since. Only recently I had to put a stop on my debit order for them to realize they owe me since last year but they saying they only owe me for this month??? Its not my fault the branch never cancelled the month to month contract. Why should I keep paying for a service I haven't been using for over a year now? I WANT MY YEAR REFUND NOT ONE MONTHS REFUND! I sent emails to the customercare email address and they fail to communicate! I went to their branch and nothing ! I try their 083135 number and they cant hear me! its a disaster this company! I will have to add this on social media and radio and TV and Print media for them to actually action anything maybe I will get my lawyer involved next.