Is it legal to provide NO way of cancelling a contract

Disgusted with Mweb. I tried on behalf of a friend who is disabled to cancel her ADSL line with mweb as she is moving homes. The website, chat facility and automated "help" line all relies on a system whereby mweb verifies the identify of the customer by sending a pin to the customers cellphone. The problem is that if you get a new cell number you are *****ed because there is no way of communicating with mweb without it. Their automated services rely solely on this. My friend changed her cell number 3 years previously. The automated call system does not have any option for this eventuality. After 2 months of trying unsuccessfully I decided to choose option 1 on their help line which is for sales. I advised the consultant of cancellation on the ADSL line, not the mailbox, and also advised of the problem with the cellphone change, on 4 August 2020 and was given reference number MWB ***9. No confirmation of this was received nor did the change of details form arrive. I called again on 28 August and choose option 1 for sales and was told that the mailbox was cancelled, not the line. The consultant refused to help me further and told me that she needed to transfer me, I asked her not to put me on the automated system because I can receive the pin. No worries she said and put me on the system which sends the OTP¡!!!!!!!! I'm pulling my hair out. Are the powers that be at mweb stupid or is this a ploy to make customers pay forever. Furthermore any attempt to email addressed to email address : *** With subject sent on the Fri, 28 Aug 2020 16:53:01 +0200 could not be delivered. The problem appears to be : Recipient email address is possibly incorrect. At the moment my friend is stuck with a bill for July, August and Sep because she cannot cancel the service, it's impossible, and she cannot cancel her Telkom line because her mweb ADSL is still open.