Unable to upgrade !!!!!!!!!!!!!!!!

I just had the most ridicules conversation with your "Upgrades department" I can upgrade my phone from 1st July 2018 and want to take the Samsung A6+ on uChoose Flexi 120 for R300 and they told me I can not. Now how can I not get an upgrade for a cheaper package? They told me that there is an issue with my payments? How can that be when Vodacom takes a debit order EVRY MONTH !!!!!!!!! I want to upgarde to the Phone that I want and NOT THE **** YOU WANT TO GET RID OF !!!!!!!!!! I will not accpet that there is an issue with my payment seeing as my account is paid in full every month on time. I want this sorted out NOW !!!!! Can someone of higher management call me that can sort this out this is unacceptable. Why do I pay for a contract every month if I can not upgrade?????