CONTRACT HAS EXPIRED

My contract has expired on 31 July 2017. I went to my nearest Vodacom shop and was told I cannot upgrade due to my financial status. I have requested them that I choose not to proceed with this contract i.e. it has expired. At the end of August 2017 I was billed for the full amount including airtime and the fee for the handset. I spent more than 15 minutes on the telephone to find out what is happening knowing that the contract has expired and I have cancelled same. Now they tell me I must pay the amount outstanding. I do not have a problem paying for the airtime I have received, but will not pay for the handset which has expired. I would like to upgrade to a new phone with the same specs of my current phone, however if that is not possible I immediately request that VODACOM accounts rectify my account reflecting that I should only pay for airtime and NOT the handset. I have emailed VODACOM regarding this and received no response. I have phoned them without any clear amendments to be made. I urgently require assistance.