MTN Account switched off for no reason!

In February I was contacted by a 3rd party to upgrade my MTN contract. I agreed and we proceeded with the upgrade, the upgrade included 2 x A14 Samsung devices and a sim for R 420 per month. From February I was billed for 2 contracts. Every month I need to phone in and correct this just for it to happen the next month again. Every month my phone is blocked and being a estate agent I lose clients and my income. This month it happened again and MTN states that owe them R 1500, I am billed R 649 every month instead of the R 420. The R 420 gets debited from my account but on my bill it still shows that I owe R 229 every month and for this reason my line keeps on being blocked. Why is my debit order correct but my account is in arrears?

Please could this be sorted I need my line for business and this is becoming a big problem.