Unfairly billed and wasnt informed about all information

I phoned customer care to find out about a bill that has been debited without consent. I was informed because I was due for upgrade and upgraded , when I saw a amount being deducted extra I phoned customer care spoke to a very rude lady that didn't want to assist and she informed me that because I upgraded before my previous contract initially ended that I am paying for my upgrade and my old installment for my phone. When I asked but why because they phoned me or let me know im due for upgrade I agreed now 2 bills are being deducted without informing me that I will still be liable to pay for the old contract as well. When I asked to speak to a manager so that we can resolve the issue and because she was so rude she put me on hold for a while. When she saw I wasn't putting down she picked up the phone and told me her manager is busy and will get back to me took my nr and put down the phone.