I had something similar happen once, when the credit card company cashed the check for a few dollars less than the check due to a misread. I called them up, and likely because I also had always paid off my balance, they recinded the interest charge and treated it as a full payment without my having to provide any extra proof ("Can you think of any reason why someone who always pays if full would miss it by less than 10 dollars?" "Um, no. Let me fix this...")