Slow loading eBay & Gumtree

Extremely slow loading on eBay, Gumtree slightly better. I've powerwashed & cleared data, done an isolation test & nothing changes. The paid computer repair man stated it was because 'the capture portal is blocked' whatever that is & the wi-fi service providor needs to fix. Went to service providor whose modem I'm also using they say no no not them go to HP, they say no no not them, I then went to Google they also say no no not them - even tried eBay in desperation - its like pass the parcel @ a 5yr olds party & no one wants to own it. Opening emails or a general internet search the speed is not a problem.

When I click to open eBay the semi circle in top left hand corner starts to spin, then stops, starts again, changes from grey to blue, disappears completely reappears as a full stop, changes to a spinning grey circle, goes backwards, turns from grey to blue & finally settles with the suitcase logo in top left hand corner of screen.

If I want to move down that listing I have to wait until everything stops before I can go further.

If I want to go back from a listing & check another have to go thru the whole routine again. The only advantage from this ritual I have time to grab a coke from the kitchen fridge & still get back before eBay loads & opens.

Perhaps someone else has had this problem - would appreciate any assistance...thks marnie