Is it always the same number, or a lot of different numbers with the same country code? In the former case, there should be an option to block and it'll vary by handset - look at the 3 dots at the top right of the screen, or possibly long-press the number in the call log (but be careful that doesn't dial it!). If you don't have that option, save the number to your contacts and assign it a silent ring tone. If it's different numbers, there isn't much you can do. Scam callers are aware that people block them and therefore tend to call as-from as different one each time.
There is a barring option on My Vodafone (online or in the app) to block all incoming overseas calls (I think). That's drastic and may not be appropriate for you.
You could also put the phone on silent at night though, again, that might not be appropriate.
