At&T Fiber 300mpbs package - Terrible performace

We had the AT&T Fiber 300 mpbs package installed around December of 2018.  From day one we have had nothing but problems and very poor performance.  We routinely get download speeds between 6 MPBS (yes, 6) up to, at best, 50-60 mbps.  Upload speed is better but I don't really care about upload speed.  Our main use is browsing the internet and gaming.

Our box/router is model # BGW210-700 with a date of 8/20/2018.  We are use an an AT&T extender, provided by AT&T; model # AIR 4920.

I have attempted to call AT&T two times but both times I was "helped" by a very unhelpful representative who insisted that I trouble shoot the issue with him/her on the phone.  I did so one time but did not receive a resolution.  The second I refused to go through the long process of "troubleshooting" on the phone and insisted that a technician be sent to resolve out issue. I was told that a technician would not be sent unless I participated in the over-the-phone troubleshooting first.   They try to claim that we have too many items connected to wifi which can cause issues, however, nothing is different from when we had the previous Comcast package and never had these issues.

This is completely unacceptable.  We received much, much better performance with out Comcast 100mpbs package that we had previously. The only reason we switched was because we currently have DirectTV which would "bundle" our TV/Internet service and AT&T offered three times the speed at about the same cost.  

Is anyone else having this issue and is there an actual resolution?   I have tried rebooting multiple times.