8ta / Telkom Mobile
Cannot change my Sim card from Data to Call

I changed to 8ta a few months ago because of their call and data rates.
Knowing that I will use my Samsung Note 1 phone mostly for internet and due to lack of knowledge, I opted for a data sim card.
That was the beginning of my nightmares. I loss reception constantly and cannot make important calls.
No reception is a lot areas i.e Klerksdorp, Rustenburg, Laingsburg etc. The list is endless.

Now I've requested that my Sim card be converted from data to a normal call sim.
They claim they cannot do it and should get a new sim and number,

Are they crazy. Most of my business clients and 1000 business cards have my current cell number.
Are they saying I should port my number with another service provider???