********** upgrade done on my 3g mobile to Samsung S7

On the 28 of October 2016 there was a ********** upgrade done under my name upgrading the 3g mobile contract that i was paying for (R75/pm) to a Samsung S7 which I do not own. An amount of R 688 was debited from my account. I then called Vodacom to report the matter and they could not even tell me who has done the upgrade. They asked me to send them an affidavit and a certified copy of my ID which i sent to ********** on the 1 November 2016. I asked them to reverse the debit and cancel that contract and it was not done. I then went to the bank to block the debit order from continuing. In October 2017. A year later in October 2017, I received a call from Burnard, raaff & assocaites debt collectors saying that I owe Vodacom an approximate amount of R 18,000.00. This is unacceptable, I really do not understand how the ***** department cannot trace who has done the upgrade. This *****ulant upgrade is probably an internal thing . How do u not have proof of the upgrade done, surely investigations needs to be done. People need to do their jobs properly c'com!