MTN contract that can't be cancelled

I opened an unlimited data contract on the 20th of December 2024,which I paid a pro rata plus January 2025 fee, the router was delivered on the 24th December and was only used from the 26 December which it connected to my work systems for only one day, which it was not compatible. Come January the 5th or 7th 2025 I received an sms saying I have used up 80 % of my unlimited data,yet I couldn't use it for my work purpose as I too it for it as I work from home, the Sim was only connected the TV streaming.on the 9th of January 2025 the service was suspended as they said I have used up 100% of the unlimited data. I have been trying to cancel the account ever since January 2025 without any success. The router was returned to MTN shop in Mams Mall on the 28 January 2025,i have been billed for March already but I don't have service. They gave me a Ref number IRMS***.Which every time I follow up I am told they are still investigating, it's a struggle to get hold of their call center as well as the agent who sold me the contract is playing hide and seek... Can I please be assisted in cancelling this contract please.