altered check

I offered an amount on a debt,$325.00 check as a settlement.On the back I wrote "endorsement of this check acknowledges you accept this amount as full payment."They used white out on the back where it was written,and deposited it.I have a copy and prior witnesses to it's original state.
Now he's billing me for the bal.
What should I do now?

[This message has been edited by silk_flowers (edited April 08, 2000).]

This sounds like an accord and satisfaction. But you don't state whether the total amount is in dispute. If the total amount owed is genuinely owed, then their depositing the check and still seeking the balance should be legitimate in a majority of states.
As to the alteration, I am unsure whwther that would invalidate a legitimate accord

The total amount never was ageed upon,but when He billed me.I said it was to much.