Vodacom over charging and Misinforming customers regarding upgrades.

I recently did an upgrade online and the sales consultant failed to inform me that I must pay for my previous device until the end date of the contract together with my current upgraded device!. So I was told by another vodacom consultant that it’s unfortunate I will have to pay for the previous device until the end date, due to the clause of vodacom, hence I’m saying that I was misinformed and it is not my fault, so I’m not going to pay! I asked the consultant to pull out the recording of the call, and apparently theres an “issue” with the system all of a sudden! And the call record cannot be pulled out! So Vodacom please inform me what’s the purpose of an UPGRADE??? If you have to pay for your previous and current device!. I then contacted Vodacom on numerous occasions and up until now I haven’t received a response from them, all I was told is that the matter will be escalated but nothing is being done.