Vodacom external sales contractor unprofessional conduct

I did an upgrade in April for two numbers on our company account Confirmation of the new charges was done in writing with the CoActivate consultant and I noticed that there was a significant difference in the charges in April. There is an annual amount increase that I understand but the remainder of the charge is for an increase as we apparently received an initial discount on the charge. This was not conveyed to me when taking out the two upgrades. Vodacom Red Business have been very helpful in following up with the external sales agent but the issue has not been resolved. The sales agent have informed Vodacom Business that I have been contacted and we are now 'refusing to pay'. I was not contacted and we are not refusing to pay. Emails to the agent and calls to the agent are not being responded to. Vodacom have been really helpful but the sales agent is now ignoring any requests for feedback from the original agent who confirmed the upgrades. Is there any way to resolve the issue that is now going on for over three months?