Horrible reception despite MTN's coverage map indicating otherwise

I have extremely bad cell and data reception in my premises, and have lodged complaints via the channels on the website but to no avail. The data speed is so bad it is basically as if I have no data. I am completely wasting my money on my monthly data bill but MTN do not seem to care! According to the coverage map on MTN's website, I am completely covered for LTE but I barely even pick up Edge! And this is on multiple devices! Appalling that I am being ********** like this.