does your payment show up in the notice? if you paid by check not putting the year or your SSN on it will cause issues. if there is a phone number on the notice you might try calling first. They may be able to track down your payment and thus you would avoid the hassle of responding to the notice. if you can't get thru you'll have to send in proof with the notice. do not send the original a copy will do. mail it so you get proof of delivery.
