BILLING FOR TWO FIBRE LINES, ******!

While I am happy with the network provider, the service I am getting from their call centre is just horrible. I have a current 200mbs fibre line at home, which is on a month to month. In February, I app**** for a contract for the same line speed, but the promo is you only pau R 99 for the first 6 months. In Feb, the new line was activated. End of Feb I was billed for the old month to month line, which I can probably still stomach seeing I app**** in the middle of Feb. I received my statement and see that I will be billed end of March AGAIN for the month to month line. How can I be billed for TWO lines at one residential address? I called the call centre and have logged numerous requests after being shoved from pillar to post. They are telling me that I need to give a month's notice to cancel the old line. How is this possible? Why is this not seen as an 'upgrade'? Vodacom just refuses to listen to me or to even attempt to understand what I am saying to them. A bunch of ****** if you ask me. Being billed for TWO lines? I took the promo so that I can save a few rands for a few months. Instead I'm being punished for taking out a contract and they are making me pay DOUBLE. Please fix this!