Good evening, what is the max speed contracted? You need to check your router settings, internet settings and finally your motherboard to see if the internet doors are 10/100/1000.

Max speed contracted is 500 Mbps.

I have logged into the router and it tells me ethernet is running at 100Mbps.

What do you mean check "Internet settings"?

I don't need to check motherboard ... my laptop runs far faster than 100Mbps.

Ok, the router tells you 100mb, have you created a new profile with limited speed or you don’t find any explication for the restriction? You have to check all settings in order to find the origin of the problem, if no success you may have to force the factory settings on the router, for that check the manual on how to do it and have your client details ready for the restart.

Even if its cat6 it can be the source of the problem

I am sorry but this is not helping. You are asking me to do all the investigation myself, and yet I have no expertise in this area. 

Hello ​@Ana Sousa Doherty,

Thank you for reaching out to us. The community shared a good help on this matter.

Please check if your computer has a 1Gbps network card and teste the connection with another ethernet cable if possible.

Can you teste the speed using another device?

Thank you

Good evening ​@Ana Sousa Doherty any news , have you the chance of doing as the moderator ​@João H. suggested?