Invoice items identification & Fees

My contract used to be with Nashua mobile before they decided to close and I had no problems. the minute I was moved over to MTN, the problems started. They billed me for airtime bought which I didn't. When I upgraded to R200 top up for 2 months I got R100 airtime and not the R200. The fees on my bill became more. I was charges twice for insurance, and a hardware fee and promo fee. When I finally reached the call center after 10 min, I am told that I must still pay Nashua mobile their insurance and their hardware fee. My assumption was that MTN is taking over my account so I am paying them. Not paying them and Nashua. I want all the hardware fees to be reversed and the insurance stopped. I also want my debit order stopped. I will pay it once I receive and invoice. This new sending invoice link to email and then waiting on an OTP that takes forever to come through is not working. send the invoice to my email straight, why does it need to be so complicated.