JPG,
What do you have? Something like one of the GO Flip models running KaiOS? Just curious. Some of the more recent flip phones on the market run AOSP (Android Open Source Project). One of those could get an app to help you block spammers more easily, or possibly implement what Dennis suggested above. If you are running Alcatel's KaiOS (French), you should still be able to individually block each spammer one by one. A pain, but it should work, I believe. Do the following steps below work for you?
From the main menu, select Call Log => select number, and options on bottom right => Call Information => select block on bottom right
You can see the list of numbers you have blocked in Contacts from the main menu
Contacts => options bottom right =>scroll down to settings => Scroll down to
"Block Contacts". This will list all the telephone numbers you are blocking.