May 15, 2015
Judging from the earlier comments here, this is most likely a scammer calling, trying to dupe people into paying on old bills that might or might not be valid.
Only you know whether you have outstanding medical bills for which you are still liable, and given that the statute of limitations on most things like this is seven years, you might be still liable if your bills are 3+ years old, but not 7+.
Still, you should not deal with anyone who calls you out of the blue: be sure to determine if they are a legitimate debt collector, calling about a legitimate debt. There are way too many scams of this type.