If you live in the United States (I can’t vouch for other countries), there are certain ways in which law enforcement is carried out, and ways in which it generally is not.
Here’s one way law enforcement doesn’t work: if there’s a warrant out for your arrest, they usually don’t call you first and tell you.
Here’s another: if you’re accused of a crime, you can’t pay a fine to avoid charges (if you can, it probably means you’re bribing someone, and they’re accepting the bribe, and you’re both in a lot of trouble, mister. Bribing the police. That’s not right!). The fines (and other consequences) generally happen after you’ve been convicted, which is supposed to occur via due process.
The Better Business Bureau is warning of an active scam that has already claimed several victims. The fraudulent phone calls use spoofed caller ID to extort “fines” from victims, by money orders and prepaid debit cards. They’ve got the full lowdown here, but the proper response is one you’ve seen before: don’t give any money or personal information (even if they have some already—victims have reported the callers having information about loans), hang up, call the real police (because others are likely getting the same calls).
The problem is that such phone calls can incite a moment of panic, and panic makes it hard to think rationally. But if you’re aware that such scams exist, you’ll be able to stop, take a breath, calm down and remember how reality works before you become a victim.