GIGAblast and spped test never goes above 250 mbps on any devices even hardwire

Been paying for gig  service for several years,,,,   finally working from home  wanted to see how i can increase speed now,   so i have he setup 

where fiber comes into home, to the thing on my wall inside,  then  new rg8 cable to  brand new  Netgear  AX5400   300.00  router 

mac that  is  hardwired  has rg8  going into thunderbolt port ,  and speed tests are even slower no then w my older Netgear r6000  ????  what am i doing wrong or  how do i fix  ??  feel like plan im paying for is not  making a difference ????