Contract Upgrade charged incorrectly as it was installed as 2nd line

I have taken a WIFI contract with Vox Telecom 3 years ago, which costed me R1159 monthly. All was good until I requested an upgrade to a business contract in November 2022. I was given a new quote of R2143 which I accepted. The new contract started in January 2023. I discovered in February 2023 when Vox tried to debit my account for an amount of R10444 when it was declined as I did not have that amount, that instead of an upgrade that I requested that Vox installed a new 2nd line which was running concurrently with the old line. As a result they were charging me twice for both January, February. Also Vox added setup fee for the new line of R2850, I did not expect this as this is an upgrade on the existing line. This is a fault on their side of installing a 2nd line instead of doing an upgrade, and now charging for both lines. Now I have a bill of R10444 which I do not agree with, Vox need to fix this from their side as I cannot pay that money. I have been in contact with Vox Team both telephonically, on whatsapp and my husband went to their offices in person but this matter has not been resolved. They have threatened to suspend my services and have done so at one point and only reinstated it after complaining. I have been promised that this matter will be resolved and that my old contract will be cancelled and they credit it back, but this has been going on and on and there is still no resolution. It seems no one wants to take responsibility to sign for the credit and rectify this mistake from their side. This is bad service on another level. Very unhappy clients. If this matter is not resolved I will be left with no option but to move to another service provider who can give me better service. Regards Glendah Mboweni