Last straw.

On 12th of July I requested a copy of my contract which I never received upon delivery as should. With my contract I was supposed to receive a free mifi router and 500MB of data. I received the router but no simcard for it, which was fine, I had to go on my own time and buy a simcard, after this was done I sent the number to the person assisting me on the 21st of July. I received no reply until 1st of August, this was also fine. The number for the router was only activated on 8th of August, this was also fine, during this time multiple emails were sent, most of the times I did not receive a reply, this was fine. So after the number was activated the courier came to deliver another phone, I was instructed to not sign and send back the products, which I did, at this point the router simcard was again made inactive until MTN received the products again which were wrongfully sent. Again, this was fine, so I see my bill on the MTN app does not seem right, I contact the people who are assisting me the whole time, where Im told to just pay and when my contract is finished they will explain to me how the process works indicating that I did something wrong. All of this was fine but when I received my latest invoice and saw I now have to pay for the FREE router and its 500MB I lost it, I have not even been able to use the router at any time. I can not understand what I did wrong. Do not know what to do anymore.