Help - about receipt number

I filed my I-765 renewal on July 23rd and I just found my check was cashed. I noticed on the back of the cleared check there is a number msc07********. I suppose that this number should be the receipt number (13 digit in total include the letter MSC) although I didn't get the receipt yet. So I went on line and check the status and could not retrieve any information. it 's said the number is not in their system. Is there anyone know about it? thanks.