I paid for AT&T Fiber Internet and the Installation Fee, but a technician never came.

Then call AT&T and reschedule. The agent will go over you the next available time. Be prepared you will not bump someone else off their appointment to get yours sooner, so ASAP is based on AT&T's schedule. We cannot do that for you as we are other customers like yourself in this public forum.

Unfortunately like many companies they are still short staffed, including techs. Too often these days reschedules are needed. However, they should at least let you know there was an issue getting someone out there so you had a chance to reschedule earlier. Though that still would require you to call, which it sounds like you haven't done.