Debt Recovery Solutions, LLC Debt Collection Complaint

Debt Recovery Solutions, LLC Debt collection department,

I do not know Cont'd attempts collect debt not owed Debt is not mine Utah

I received - threatening letters from Debt Recovery Solutions, LLS, with a contact name of - -. Both letters claim they purchased my debt from -, a place in which I have NEVER had a credit card or any type of debt. In both letters, they prompt me to pay immediately, etc., at the bottom there is a spot in which you can enter your credit card number for payment, and you also have the option to pay online. This is an extremely unfair and bullying type of practice. Plus this debt is not even mine. If they are going to send out letter such as these, is it legal to send this type of letter without including legitimate proof of the debt?