How Long Does It Take For Credit to Post to Cell Phone Bill

I was speaking to a representative last night about a billing issue. He told me that I would receive a credit on the account to resolve the issue and gave me the reference number    

I received a text this morning saying "ATT Free Msg: We've completed your request  ."

So far my bill has not changed and I'm slightly concerned I didn't receive the credit. Can you confirm that a credit was actually issued in association with the reference number above and let me know when I will see it on the bill?  [edited for privacy – please do not post personal information]