I just upgraded my internet plan from 25/5 to 100/40.
On a laptop connected by ethernet i record a download speed of 80 - 100 using fast.com
On my android tv Mi Box connected by wifi i also record a download speed 80 - 100 using fast.com.
So I'm quite certain that the plan upgrade has gone through and it is achieving the right speeds.
However on my S8 plus (even if next to the router) i only record a download speed of 35 using fast.com
On my Inspiron 5675 connected by wifi, i record a download speed of 28 using fast.com (but it is upstairs).
I also tried speedtest.net and the results were the same.
I only have one router, access point and SSID — is there any possible things i can try to get higher speeds on my phone and desktop?
do you have a dual band modem? possibly try the other band.
Have you tried deleting the wifi connection on your S8 plus, shutting down the phone, restart phone and reestablishing the wifi settings? (turn is off and on again)