Doctors office sent me a bill a year later?

I got a call from a collection agency to pay a $30 copay. I guess at the time they weren't able to collect my copay in person, but I'm a little irritated they didn't just call me and say hey we still need you to pay this. What would happen if I didn't pay this small of an amount? I called the doctors office and said i'd pay them over the phone, but they said they couldn't do that and I had to pay the collection agency directly. Honestly, if the doctors office already wrote it off as a loss, then what's the point of paying?

Doctors office sent me a bill a year later?
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