Poor administation

I was contacted today by call center debt and were informed that I need to pay R300.00 due to 4 Months payments not received on my SABC TV License account. Reason being that I changed bank accounts in the month of March 2018. I contacted SABC TV Licenses on the 29 March 2018 to inform them that my account details has changed and that they should update their system with my new details. I have been struggling to get through on their telephone number ********** since March which is not my fault! I can't pay wait 20mins plus for someone to answer the phone as I am phoning from my mobile phone and would like to know if SABC will pay for these calls. What I can't understand is that I have never skipped even 1 payment but due to me changing my account details and trying to inform them of it, it resulted in non payment for 4 months which I calculated as follows: R28 x 4= R112! So how did SABC get to the amount of R300 + that I owe them now and how come did SABC not contact me to find out why they have not received payment after the first month of non payment. No SABC just decided that they will not go the extra mile and will just proceed to hand me over for such a ridiculous amount! Surely someone at SABC must be able to contact me and assist me to update my details with them?!