Recently received an alert regarding my credit score with an unpaid medical bill of $109. I had a score ?

Of 773 as 5/28 and now it dropped 77 points. I didn't receive any notification or the actual bill. After having my baby I made every effort to pay my out-of-pocket expense of $4000 by calibrating with insurance, hospitals and doctors so I had no problem in paying a bill of $109 if I had received it. What recourse do I have now and what steps should I take to correct it? I've researched online and there isnt any information with a detailed process. It's to the point that I'm confused now. Should I call the doctor or collection agency or both? Do I dispute send a letter to credit bureaus while going the dispute?