Failed to get game data from server??

Niantic say you're "not banned"? Really?

... must be a temporary ban meaning you'll get your account back in 2-4 weeks and no sooner. That's how long most people I know of had to wait to regain access to their accounts. It really all depends on the reason for the ban.

Have you tried to login with a different smartphone?
If not I would suggest that you try with an expensive one like Galaxy S7+ or iPhone6+. If those have enough memory left and yet aren't able to connect to the server while beeing in WiFi (/Wlan) then you at least know that it's not an issue with your device. If they are able to connect via WiFi/Wlan then try via a mobile connection next.

(I assume you have already tried to connect with you device via Wifi/Wlan. It might help to change the Gps settings from accurate to "only via GPS")