Trying to ping 8.8.8.8 is not really a good way to find out if there are issues.
ICMP (ping) isn’t TCP nor UDP. So it might get handled differently by the network.
You could try to use iperf (iPerf3 for beginners - #2 by admon) to test the speed via UDP between both devices.
8.8.8.8 is Google, so it’s mostly higher prioritized within the Vodafone network. They are doing so many shady things to keep the network up and running without investing into the backbone 
Switching to TCP could (!) solve the issue. But TCP is only available via OpenVPN.