Long waiting time to talk to manager on telephone

I moved house in July 2015 and moved my Telkom landline at the same time to the new address. However, my monthly invoice still reflects the old address. I've tried several times to change the address to the new one but it has not been resolved. Today I finally (after being on hold for 5 minutes) managed to get through to someone in the Telkom call centre who says they updated it today but it will only be effective from my April 2016 invoice - even though it should have been updated last year- I asked to speak to the manager - he took 20 minutes to come to the telephone. Then he refers me to another department where I have to start the entire process over again (from being on hold again). Very Poor service.