Article 3 of Commercial Code Case

A bank holds two promissory notes, Note A has 5,000 balence and note B has a 10,000 balence owed. The debtor on both notes pays 7,000 and a clerk in bank sends back both notes marked '' paid'' by mistake with a letter thanking customer. Six months later the bank demands the 8,000 balence on Note B and the debtor produces the ''paid'' notes. The bank proves the clerk was not a bank officer and had no authority to cancel notes. The debtor admits only 7,000 was paid, but still claims both notes were cancelled.

Was note cancelled? Why/Why not?
Will Bank get 8,000? Why/Why not?

Refer to cases/rulings to back up answer.