Ok so I am having the same problem which has been really annoying! I have spent over 4 hours over 3 days on the phone to Apple repeating the same steps and taking the same screenshots to get no where further. I just managed to fix this myself, hopefully it works for someone else too!
I borrowed my partners phone, disconnected Wi-Fi so only cellular data was on and signed in to the app store with my account. I tried downloading a free app which gave me a pop up to confirm the terms and conditions. This came up blank again but I scrolled down the page, as previously suggested, the writting started to appear and it allowed me to confirm the terms in the top right corner.
During this I signed out of iTunes on my iPad and it would not let me sign back in telling me the iTunes store is unavailable to process purchases at this time. To fix this I turned Wi-Fi off on the iPad and connected to a mobile phone by hotspot (with that Wi-Fi off too) i then signed in to the app store and in to iTunes in settings and all worked again!