How To Avoid Gettin’ Scammed:
If you don’t recognize a number, don’t call’em back.
If you really want to call back, Google the number first. Check the area code to make sure it’s not long-distance. Check the full number, too; in many cases, you’ll find a page full of results saying “Do not call! It’s a scam!”
If you’re an Android fan, try to get on a device running Android 4.4 (KitKat). It has a built-in number identification system, and it works quite well for at least identifying legitimate, non-scammy phone numbers as safe to call.
Check your phone bill for sketchy charges. Your carrier knows aaaall about scams like this, and will generally reverse the charge if you complain.