Had a hospital bill go directly to collections aft...

Had a hospital bill go directly to collections after I did not receive a bill. They call me in September of 2019 and I ask these guys to just bill me every month. Nothing comes in the mail. Then, mid-2020 the collection comes off of my credit report. Wonderful, right? All of a sudden, after checking my credit report yesterday, they pop right back up without warning like bad acne. You would think that they would at least send SOMETHING in the mail or try calling.