REALLY UNSATISFIED WITH VODACOM

I've been a loyal customer of vodacom since 2010, in 2014 I changed my debit order date to the 7th of each month due to my new employer paying on irregular pay dates,vodacom client care consultant didn't give me the right info on when they would debit causing my account to miss payments,at the end I paid all outstanding amounts and ever since I've been paying extra on my account monthly and never pay late. My contract is now due for an upgrade and I would like to upgrade to a tablet but vodacom is declining my upgrade due to negative payment history which is making me very unsatisfied because after many years of staying with vodacom and being a loyal paying client, this is the service I get back from vodacom.I would like for somebody to assist me with my upgrade because this service is unexpectable.