MTN is useless

During January 2024 I went to the MTN store in Harvest Place, Kempton Park, to upgrade my existing wifi contract. They did not have any routers and I said that I would wait for a week. On the 28 January I went back to the store but they still had no router for me. I then went to ER Mall in Boksburg who assisted me. It was explained to me that I would have to give a month's notice on the contract BA***. They submitted the notice and I was informed that I would still have to pay at the end of February 2024. I accepted this and left with my new router. The old router was disconnected, by myself on the same day and has not been switched on since. I was billed on 27 February, which I accepted but on 30 March I was charged R598.00 which was the contract amount. I phoned the call centre on 135 and spoke to a very helpful lady Ms Damon, who told me that there was no reason to bill me at the end of March and told me that I would get my money back. A reference number *** was given to me. I waited 2 weeks and phoned 135 again to follow up on my refund/credit. I was then informed that the billing date on my contract was the 27th of each month and that I was therefore 1 day late in January to give notice. The billing was therefore correct on their side. How is this possible? Does integrity and honesty, linked with common sense not exist within MTN? Their service in my opinion is pathetic. I have had my existing phone with them since 1995 but clearly this makes no difference to them.