My internet is awful and so is my mobile service

I recently moved to a property that is contracted by Xfinity but my unit is in the basement. I was forced to get the fiber glass internet because nothing else worked here and now I get splotchy service, my account says I should have a complimentary wifi extender but the technician did not leave one for me and when I asked in the chat they wanted to charge me for it. My cellphone which is also through Xfinity on my parents account gets no service and around the property even when I’m outside the basement I can’t even connect to Xfinity mobile WiFi. When I drive out of the building I have zero signal for about 3-4 miles around this area…HELP!