Fraudulent incoming and outgoing calls

I am getting 50+ fraudulent calls a day each from a different number. (No one is ever on the other line). It seems that through this activity they are also gaining access to my account to make calls, tons of them I guess because Ring Central has now billed me twice in 3 days for call overage charges. The chat line has no idea how to deal with this except to change the phone number I have had for 7 years. There must be some technical way to deal with these fraudulent incoming and outgoing calls??