Problem with MTN overseas.

Preparing for a European visit, I contacted the MTN Shop at I'langa Mall in Nelspruit and asked them to make sure that I could use my phone when overseas. A salesperson took a long time fiddling with my phone and scrolling on his laptop. I asked him if he was sure it would work, and he confirmed that. However, the phone did not work at all during my rip, not for phone calls nor for internet use. I tried all kinds of settings, but no luck. The most common error message was "Not registered on network", but I also got "Your SIM card does not allow that". I have had my MTN contract for 20 years and have been quite happy with it, but this experience disappointed me.