Parental controls keep blocking homework sites on Nexora broadband

Hi all, hoping someone can point me in the right direction because I'm about ready to throw the router out the window. We set up parental controls on our Nexora broadband yesterday for the kids, but now it's blocking random stuff like BBC Bitesize and a maths homework site. I assumed it would only stop the obvious bad stuff. I've tried turning the filter from 'strict' to 'standard' but it still seems over the top. Is there a way to whitelist certain sites? Or is the only option to switch it all off, which seems a bit pointless. We're on the Home Fibre 500 package if that matters.