Should you experience problems with connecting to a VPN on iOS or Android devices via PPTP protocol, first thing to try would be L2TP protocol. Should you also experience problems here, it’s time to use OpenVPN.
On iOS, you need to have a jailbroken device. On Android devices, there are 2 ways to connect via OpenVPN; one without need of root access using FeatVPN (a tutorial for this will follow) and one where root is needed. Find the instructions here: