Still charging for cancelled contracts and no response

I have emailed and phoned MTN on numerous occasions to cancel two cellphone contracts that two years contract is completed on the 25th October 2020. We are still been billed every month. Despite calling and emailing I have had no response. I am in the tourism sector and have had to retrench all staff and struggling to maintain core business in order to restart. When all other entities have been willing and able to accommodate small business I feel that corporates like MTN are out to exploit and ***** from ordinary people using COVID as a facade to hide behind and offer very poor service and not respond to emails or phone calls.