<prompt> Human: I am a Canadian citizen who did some small consulting contract work for a US federal agency in 2014. I filed US and Canadian taxes for 2014. I sent payment in full by cheque for my US federal taxes with my 1040NR and request for ITIN Individual Taxpayer Identification Number. I couldnt pay online because I didnt have a SSN or ITIN at the time of payment. I also paid US state taxes by physical mail, but that went through fine and I dont have a problem with those.The IRS deposited the cheque in April 2015. They sent me mail in approximately October 2015 telling me that I owed them the amount equal to the cheque they had already deposited. I called them and they claimed that they had received no payment. I mailed them proof from my online banking that the cheque had been deposited by them.They continue to send me mail requesting payment. Ive called them again and they cant find the payment I made. What else can I dosend them? The payment theyre requesting is about 500 USD.  <response>: Call your bank, get a copy of the cancelled checkque. Continue to send that as your proof as it is your only proof of payment. 