I am trying to enable a VPN connection from a MS Surface to a Windows server using an iPhone hotspot on the Vodafone mobile network but haven't been successful. I can browse the internet fine using the tethered hotspot.

The VPN settings are PPTP, optional data encryption, and MS-CHAP v2 authentication protocol. These settings work fine when connected using wifi, and also when tethered to a Spark and a 2Degress mobile hotspot, just not the Vodafone mobile network.

I initially was getting an Error 806 but after trying various settings changes, including the APN, I am now getting an Error 800. Investigating these errors indicate the most common cause for this is that there is at least one internet device between the computer and the VPN server that is not configured to allow GRE protocol packets. It requires TCP Port 1723, IP Protocol 47 (GRE) to be allowed through. Given that it works fine over other connections it points to it being either something on the phone, or the Vodafone connection.

I have spoken to Vodafone and their Technician said that they place no restriction upon the Network - if you can connect to the Internet via a Hotspot then you should be able to connect to your VPN.
He also the issue could be the authentication of the phone against the VPN and not the APN setting as he did state that there have been no changes to the Vodafone APN settings. Given that it works fine over other connections this seems unlikely.

Appreciate any thoughts or assistance in getting the VPN connection working.