HELP PLEASE - poor wifi coverage with Fiber plan

​I'm currently on the 1000 Fiber 1 GIG plan and have been on this plan for about 5 years.  I've always been told that fiber is very fast internet but I've had nothing but poor connection problems from the beginning.  All of my devices that are hardwired I have zero issues, it's everything else that's relying on wifi.  We currently have 3 Airties extenders around the house, which helped a little, but there are still multiple "dead" areas in the house.  We have poor cellphone signal in my area so we have to rely on wifi calling, but most of the time I cannot complete a phone call without it being dropped or the other party not being able to hear me, which is the main reason why I haven't been able to call AT&T for support.  I cannot watch a video on my devices without it freezing or lagging out if I have an email or notification coming through.  Restarting my router takes at least 20-25 minutes to fully boot up, but sometimes I have to restart it 2-3 times just for it to get the internet working properly.  It is very frustrating as I work from home, and being able to take phone calls and have steady, reliable internet is an expectation.  Just to give you an idea, according to speedtest.net my current speed is 3.13 Mbps for download and 4.03 Mbps for upload.

I'm at my wits end, any help at all would be greatly appreciated. ​