Upgrade of contracts after 2nd and onwards upgrades with Vodacom contract phones and pay the handset for 27 months

I started my contract with Vodacom in January 2001, after 21 months I upgraded the contract and it then moved to October every 2 years that I upgrade my contract. I have a few contracts with Vodacom and they all have been upgraded more than once. I upgraded 2 phones on the 18 October 2015 (info from Vodacom Upgrade department), My son went to upgrade 1 phone on Sunday 1 October 2017 and the Voda-shop consultant said that he still needs to pay 4 installments on the hand set as the contract only expires in January 2018. I phoned Vodacom on 082 111 and talked to vatious people on the matter that the contract is already 23 monts old and why sould I pay extra for the handset untill January 2018. They said that there system shows that the contract started in January on there system and that why I can upgrade every two years in October. This works out that all contracts then runs for 27 months and not for 24 months. They said that the system don't update if you renew the contract, how many people pays extra for 3 months on the upgrade when it is due, I have for the last few years always upgraded October every 2 years and have paid 3 months extra in the past not thinking of this problem on hand. I am waiting for Vodacom's back office to respond about the query I logged and they will only reply between 1 to 7 days from 2nd October. The question remains at this stage how many people that has contracts with Vodacom is paying the extra 3 months after they upgraded after 24 months as this seems to be the case. I would like Vodacom superior people to give the answers and not someone at a call centre that only works with what they see on the system, I have to mention that I spoke to various people and one Line Leader for more than an hour and a half just to hear the same thing over and over and when I asked how many monts it will be from 18 Octobet to January 2018 they give the answer of 27 months but keep on saying that I have to pay the 3 extra months installments. Maybe 1000 or 1000 000 people is paying this with out knowing this and Vodacom gaings lots of money this way, I wont know maude they owe me a few thousand rand.