Your Telkom app problem sounds like this
https://mybroadband.co.za/news/security/211576-telkom-systems-crippled-by-wannacry-ransomware.html but they are supposed to have resolved the issue, I'd try reinstalling the app first. If that doesn't work then sorry, your only options are to either wait it out until Telkom fix things or talk to them.
For the landline, you'll need to fill in this form
http://www.telkom.co.za/today/media...ice_Cancellation_Form_V4_final_20151119_1.pdf then sign scan and send it to
servcancellation@telkom.co.za
When you send the cancellation, you should get a response with a reference number. There is a 30 day cancellation period, so you'll only be able to complain on your second bill after submitting the cancellation. Chances are that second bill will still have the charge for the landline, if not your one of the lucky ones. If you are still being charged, send them an email quoting the reference number you received and just keep doing that after receiving each bill until they eventually cancel the service.
For me, it was cancelling my ADSL line after moving to fiber and after 3 months, the line was finally cancelled. As always with Telkom,YMMV