If it's a legit collection agency they will be polite and courteous, if they expect to receive any payment of any real debt owed. If they are rude and crass from the get-go, they're something wrong and could be a scam or phishing. Otherwise, it could be harassment if they break any of the rules, could report to the FCC or get a lawyer, etc.....
I was getting a lot of hang up calls and wrong numbers for the cell phone number that was "recycled." This is a big problem, nowadays.
I found something that really works. Forward all your calls to voice mail and use the generic voice message that doesn't state your name. They usually do not leave a message if they're not legit. If they are legit, they're usually extremely polite and friendly and professional.
On Aug. 15 and 16, about five calls a day starting just after 6AM; same calling pattern as 614-729-6042, which seemed to replace this number for the next two days (17th and 18th)
They called my house 4 times yesterday starting at 8am and did not leave one single message. I hate telemarketing! I finally answered it and it was some recording telling me to hold for a non-sales, very important phone call. I just hung up with a few mutterings of vulgarities.
This phone number is from the World Financial Bank, which in my case means Limited credit card. If these people are calling you it means you have not paid your credit card.