How do I prove that I am not responsible for debt owed 20 years ago and after the death of my husband 8 years ago?

Any debt that exceeds seven years in age is, by law, no longer valid. I am not sure which legal statute you need to cite.

It is likely that someone bought this debt for pennies on the dollar and are now trying to collect, but they have no legal standing to collect such a debt!

This is actually a legal question which should be posted in the LAW forum.