Not honest or transparent

So I took out a new LTE SIM card with router package with mweb the next day it was on promo for the first 3 months for free I phoned mweb as my product hadn't been activated yet and they said that they would credit my account so I can also be included in the promo anyway to my surprise they sent me a invoice for the full amount so I called and the accounts department said they can see on the system that the promo needs to be activated but I must please understand that they are very busy two days later I received a invoice for the next amount plus the arrears and it is impossible to get hold of their call center as the waiting time is ridiculous I have waited on a call over 45 minutes and still haven't got through look the internet is great but I am on the verge of leaving them if this doesn't get resolved.