I had a similar attack of spam calls for a while. It started the moment I answered one call and continued for months. Simply not answering was not enough. Blocking specific numbers does not help either because they change every time. I then blocked all calls not in my address book for a few weeks and that helped. I could then disable the block again and for a year only got an occasional call here and there but could ignore it based on the area code. Now it finally seems quiet.
I’m on an iPhone. Could not find any other way that would help me block spam calls that is not expensive and/or privacy invasive. So blocking everything is the only option.