If its calls coming into your main phone number you may have to shield everyone behind a phone tree/dial plan. Spammers wont be able to select 1 for dept 1, etc. The same goes for direct dial numbers. Set up a dial plan for each direct #, make the caller press 1 to connect. Would only need to be for a few weeks, eventually the calls will stop once they get no human voices to answer their calls. The filter wont work if they are spoofing phone numbers.
Fingers crossed for you! this can be very frustrating to deal with.