Terrible service! Consultants don't know what they are doing!

I have two contracts under my account. Two years ago, the first upgrade was done in April 2015. This year, I upgraded this contract in May 2017 and then noticed that on my statement I was still being billed for the old handset. Upon contacting the call center, I was told that this was due to an early upgrade. Correct me if I'm wrong but how is April 2015 to May 2017 less than 24 months???? How is this an early upgrade? And how is it that upon upgrading, I was not notified that this would be an early upgrade (which it is clearly not if you do the math) - now it seems that the second contract on my account is also being billed for "early upgrade". How is this possible? I have dealt with multiple consultants who all gave me different stories, reference number, escalation number after the other and still this has not been resolved. I need to know why this was considered an early upgrade when the period was from April 2015 (iPhone 6) to May 2017 (iPhone 7) and why is it that no one at vodacom can give me the same information? Everyone in your call center passes the buck and transfers you to multiple departments until they eventually give you empty promises to call you back and never end up doing so. I am growing extremely fed up and I feel that at this stage I will never recommend vodacom to anyone.