I suppose it could be some sort of generic load balancing Traffic Management, which most networks have in some form when capacity is constrained, although that wouldn't explain why the VPN is faster (you don't indicate above which of the new tests were via VPN and which weren't?). I suppose the VPN could also be taking a different route (peering / routing) to give a better result.
I'd be inclined to find a server IP that this can be tested against, then you could run a traceroute both via Voda and then the VPN to see what differences there are in the server hops. Can you replicate the issue elsewhere, such as via a big file download server/site like Microsoft?
Thanks for your quick reply.
After speaking with Vodafone's technical team regarding faster speeds on a VPN they say it's non-sense and say "We don't throttle you" bla bla bla, you are not connected to the vodafone network with a VPN etc... It's normal to get 10Mb/s or under on a speedtest on 4G based on your area etc.
I have actually done a traceroute against a server to google before I'll copy the results below this was without a VPN I haven't performed one with a VPN yet but I can do that later if it will help.
Tracing route to google.co.uk [216.58.213.3]
over a maximum of 30 hops:
1 1 ms 1 ms <1 ms 192.168.42.129
2 * * * Request timed out.
3 71 ms * * 192.168.213.21
4 39 ms 40 ms 38 ms 192.168.213.22
5 * * * Request timed out.
6 * * * Request timed out.
7 41 ms 38 ms 41 ms 63.130.127.221
8 60 ms 40 ms 37 ms 90.255.251.18
9 38 ms 39 ms 40 ms 108.170.246.161
10 46 ms 40 ms 40 ms 172.253.65.211
11 57 ms 42 ms 38 ms ber01s14-in-f3.1e100.net [216.58.213.3]
In all tests 2,5 and 6 all request time out.