I have contacted their customer support on every occasion but they are not really any use on this issue, I don't think they encounter issues relating to usage abroad very often. So the advice is same every time: set SIM to outside UK, take SIM out of phone and restart the phone. This has never worked yet, I even had a replacement SIM sent without success... Luckily my phone is a twin SIM and I use my alternative during my trips, but I felt it was important to warn other potential users of this issue before signing up to VECTONE if they intend to use it on their travels.
I am not a technician but this issue seems to me as relating to a network partnership in the international roaming world?