Automatic Contract Cancelation

I've been trying to take out a contract with vodacom. After being approved and selecting a phone all I had to do was accept the debicheck mandate on my banking app which I received on the 18th of October. Unfortunately I was unable to do this. Everytime I tried to approve it, I was given a verification error. I immediately called vodacom and was told someone from that department would call me back. They never did and the mandate expired. On Monday the 21st, I used their tobichat to get an update and was told to contact my bank. During this time I received 2 missed calls from vodacom but was unable to answer as the phone would ring for 2 seconds, not giving me enough time to accept the call. After contacting my bank they told me it couldn't be verified as there was no installment amount on the mandate, only an initial amount. They then advised me to contact vodacom to cancel that mandate and resend it. I called vodacom and explained the situation as well as why I couldn't answer their calls. This is not an issue with my phone as I can answer calls from everyone else. The consultant on the phone made a note of this and said to be patient, they would call me back. They never did and the debicheck expired later that evening resulting in the contract being canceled.