MTN Top up Contract billing

I have been an MTN top up customer for the past 10 plus years. Each and every year l use roaming services that have the same terms and conditions of a top up contract. In January 2021 MTN sent me a bill Of R9 900 stating that l owe them . I phoned 135 numerous times , visited all the MTN branches in Bloemfontein but still no explanation no solution. I even sent emails to MTN enquiring the case with no response. On 25/11/2021 , l received a call from my banker informing me that MTN has handed me over and l am now blacklisted, just like that , no explanation , no response to my query . I want to cancel their contract immediately l am so hurt and disappointed . MTN Managers please sort my issue out and respond to my enquires , l am currently going to take this even to the newspapers , PLEASE CLEAR MY NAME. MTN Contract reference BA***.