If it's showing up with the + prefix, that usually means it's coming internationally (at least, that's been my experience as a US-based user). I'd imagine you could block international calls from your carrier, if you don't normally place or receive international calls in the first place.
You can try nomorobo. It blocks spam calls before they ring on your phone, usually. I've been using it for about a year now and it works pretty good. I rarely get a spam call anymore.
That app seems to be region locked. Also it probably uses a database that checks if the number is spam or otherwise. I just need a simple prefix blocker preferably foss.
You can do it via macrodroid
I am now trying simple dialer from F-Droid. I'll see if I applied the blocklist correctly.
I'd also like to block all codes from my same area code (nobody has my area code except spammers)
I use AGcontacts, not foss but it does allow me to block all calls by the area code (first few digits) eg 02* or 017*.
It's been working fine so far - I know a lot of my spam calls have certain dialing prefixes, and if it happened to just be anyone I know, their name would display - so I can call them back.
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