Vodacom charges

Two years ago received a new (upgraded) phone on 1March 2013 (invoice date). Started a new contract in February 2015 as an upgrade. Was told today by Vodacom that I will have to pay for two handsets in March 2015, being the old one and the new. The reason is that the old contract was for 24 months and March to March is 24 months. I pointed out that it was actually 25 months. March to February is 24 months, so they were actually going to be charging me for March 2013, March 2014 and also March 2015. Then the not so smart lady told me I was being charged extra because I had renewed my contract 3 months early and I would still have to pay for the old phone for this additional period When challenged about this 'fact' of being 3 months early, she denied saying it. She also told me that the account number printed on one of their invoices which I had, was invalid and didn't exist. What an administrative shambles. So now I have to pay extra because Vodacom can't read a calendar. Guess where I'll be going when this contract expires!