its not perticularly clear whats running slowly , is your internet being slow on the pc from the phone , but is fine on the phone itself , or is the pc in general being slow an thus making the internet slow as it cant open the browser at the usual speeds
general maintenance of the pc has not been undertook and needs a good service , would help in general
adding more programmes to try fix it will also slow your computer down more so dont be fooled into getting more antivirus etc
have only one antivirus that works on the computer ,
have the least amount of background programmes running
clear your startup programmes ( consult google or someone who may know more about computers ) as its a technical thing to do and can mess things up if done incorrectly
in the case of it just being the internets slow , try a few things such as changing the web browser your using , i find that google chrome is really bad at times for loading things , ive always used firefox but that can be slow to so trial and error here is a possibility
otherwise without physically going through troubleshooting on the pc myslef its harder to diagnose as its a connection issue , im aware that mobile internet providers , if you use alot of download usage (not over the limit just alot) they tend to cap your speeds to allow fair usage to other people in your local area
on your phone its optimised for mobile websites which are much smaller and less data to transfer so naturally would seem faster than it loading on a pc
my guess is thats whats hapening here , you usage speed has been capped temporarily for that term of payment that oyu have currently