Wrong Billing

i write to report that last year in April i upgraded my contract and request the agent to give me a 12 months contract,but the agent put me on a 24 months contract and upon realizing that i phoned the call centre and the matter took time for cellc to rectify.The matter was rectified in July and according to my knowledge my upgrade date is April not July.Now cellc is wrongly billing me as they are saying my contract started in July not April.I now have to pay for the gadget i received in April 2014 up until July,is like to them they are no longer considering subscriotions that i paid in April up to June.<br> I phoned and promised to rectify the matter but up until today nothing has been don.