Bad service

I sent in my Huawei P9 for a screen replacement beginning of September, when we took out the contract they said we get 2 FREE screen replacements. MTN said that Huawei does not have any parts to fix/replace the screen and that they had a few of them waiting to be repaired/replaced. Now we received a quotation from Huawei for the replacement of the back cover???? The back cover does not need to be replaced/repaired, it is the screen. MTN phoned my husband and said that if we do not pay for the back cover, they can not replace the screen? This morning I received a call from MTN saying that the frame is bent, and I need to pay R1849.01. So I asked her how does this work. First they phoned my husband and said the back cover is R1849.01. We sent in the phone for a screen replacement, there was nothing wrong with the frame or back cover. The lady then said to , So I must reject the quotation, so I asked her how is it that we must pay for something that was not broken? This is pathetic client service from MTN and Huawei. I will not pay R1849.01 for something that was suppose to be free?