I can't call one particular number

This is more of a suggested answer than a question. I've been having the infuriating problem of not being able to reach one particular number, it was going direct to voicemail. I wasn't blocked, there were no diverts set up on the recipients phone and Do Not Disturb was off. I've been through the usual restart on my iPhone, SIM out, etc. and so has the person I'm trying to call. It was driving me nuts because this person was one of my emergency contacts. Someone suggested it might be a routing problem with the network and to contact my service provider (Vodafone UK). They didn't acknowledge they knew of this issue but I finally got someone on their Twitter help team who suggested the following:  Both people should do this. Go into Settings > Mobile Data > Network Selection > Turn off Automatic > Select Vodafone UK from the list and then restart your phone. This has worked for us so I thought I'd share in case it can help someone else.