How do I unblock my iPhone blocked by scammers?

If you mean that you logged into someone else’s account on your device, you’ll need them to unlock it. If you have the original receipt from Apple or an Apple authorized reseller, Apple may be able to assist in unlocking your device.

If what you are telling us is accurate, they have already tricked you into logging into your phone with their Apple ID, and they have already taken advantage of that to "limit" your device.

If you are the original purchaser of this iPhone, and you have a receipt from Apple or Apple Authorized Reseller clearly showing your name and the phone's serial number, you can submit an Activation Lock Support Request. Apple is not obligated to grant such a request, but with proper proof of original purchase, they might.

How to remove Activation Lock - Apple Support

Absent proof of original purchase, Apple will not remove the Activation Lock. Paying the criiminals is not an especially attractive option either. You would be rewarding crime, and even if you paid, there would be no guarantee that the criminals would release your phone. They might just take your money – then attempt to force you to pay even more – or simply run with your money, leaving you with a "brick".

If this is the scenario that applies to you, you may have just learned a very expensive lesson about never allowing anyone else to log into your iPhone (and never logging into your iPhone "temporarily" with their Apple ID, another variation on this scam).

If it is now locked to someone else's Apple account, your only option is to present Apple with the original proof of purchase in your name from Apple or an authorized retailer to have the activation lock removed.

If you do not have the original proof of purchase, there is absolutely nothing you can do. It is useless. Recycle it and buy a new phone.