Vodacom - paying for handset after expired and being billed double

Hello I had another cellphone account on my mothers name and the contract expired in mid year 2019. We visited a Vodacom shop and asked what will happen with the contract when the 2 years is finished. They informed us it will automatically change and we will only pay for a data/airtime contract and not for the handset anymore. My number and this additional number expires the same time. My number this is what exactly happened, I stopped paying for the handset. The additional number on my mothers name, continuous to charge for the handset even after the contract expired. I asked my mother about it however did not get any outcome on it. Because I am not getting any solutions on it, mid December 2019 I went to Vodacom and transferred the number over to my name. I asked about the handset still being charged. They informed me to transfer to my name and then query it with client care. On the additional number my mother was still debited for December bill. January Vodacom mailed me a statement with the December still outstanding account. I called Vodacom client care, the agent that assisted me could not help me regarding the additional number paid in December and being billed again in January. I asked her how long the turn around time will take and she informed me she cannot tell me how long my query will take. Do you not have a standard of example 5 days to come back to a client? I said to her I have another query regarding the handset being charged after the contract expired. She informed me I had to tell them. I asked her who is them and she firstly said the Vodacom shop I visited and then the upgrade department. The agent on the line could not help me with any solutions or assistance. She actually provided me with more problems. Vodacom does not offer any email services to launch a complaint and to call the client care does not assist you.