I saw you already blocked the individual numbers one by one, but it will be a pain in the ass to keep doing so. You can set up in your settings to silence the unknown calls: Detect and block spam phone calls. https://support.apple.com/en-sg/HT207099 or use third party apps to filter and block the unknown numbers:
How to stop annoying robocalls on your iPhone or Android phone
https://www.theverge.com/21327304/spam-call...-iphone-android