Pay the bill, stupid!
Paying a debt you don't owe is like hanging a "Kick Me" sign on your record for all these bottom feeders.
Maybe the bill had already been paid but improperly recorded. I’ve had that happen several times. I also received bills for body armor that I did not order nor did I pay for it. I ignored the repeated bills and waited for them to try to contact me by phone which they did. The bill was for a police officer in another state with exactly the same name (not a common name either). The idiot collection agency simply did an internet search and found my name; assumed the customer was me even though they sent the product to another state. I have also had bills sent to addresses other than mine and I did not have any way of knowing that the bills were due or past due.