What happens to expected credits on my account when I cancel my service?

I recently had some billing problems with AT&T and am expecting to have the issues rectified through credits posted to my account next month. However, I have to cancel my service due to work before the end of next month. How will those credits be attributed to me/fulfilled with me leaving AT&T? Considering the billing problem was on their end I would expect to be given back the money in some way.