[Client] "Purchase RP" Tab in Store is Broken

For the last few patches, I have had a problem where I could not access the store. 2 or 3 patches ago, I was able to access the store again, but only at seemingly random times. Any other time the client would be black where the store should be or it would give me a Session Expired message (Each patch it seems I am more and more frequently allowed into the store). However, whenever I click the Purchase RP button nothing happens, and from there on every other shop tab I click on all that appears is a white rectangle until I restart the client.

NOTE: I DO have Avast Antivirus, but turning it off or putting the store url in my exclusion list seems to change nothing. I have also tried the other things the help page tells you to do if your shop stops working, such as resetting IE. I have checked and this also occurs on my alternate account that I use to play with low level friends. As another side note in case it helps, I am running Windows 7 and Microsoft Security Essentials is installed but everything is turned off.

EDIT: Tried this on my other computer, and the same thing happened.

EDIT 2: I tried switching to my phone's hotspot, and boom! First try, both computers can now access the RP tab with no problem, and I was even able to redeem that RP card. The **** gives, Cox?

Edit 3: From some quick research, it seems cox has heavy filtering on port 80 (HTTP), and for some reason it feels the need to block the league of legends store... I forgot to mention in edit 2, but after changing to my hotspot, I could ALWAYS access the store as well.