Is this illegal

I had a debt charge off about a year ago for $3,900. The debt then went to three different collection agencies all of which could not properly validate the debt ofater i sent debt validation to all three of them. It then returned to the original bank who said i was liable for the whole amount. Isn't this illegal for the bank to try to collect the debt from you after they have declared it as bad debt and cahrged it off. It has now gone to a fourth collection agency who will receive a debt validation from me.