Hello Tuyenpham,
Welcome to the community!
You should note this forum is community-driven and not intended as a venue for customer services so we would not have access to customers' accounts. Unfortunately, we would not know what was previously discussed. As far as I am aware, though, a credit balance will be mailed out to you 2 to 3 weeks after your last bill had been generated (see here). However, that does not mean you would receive it in that amount of time. It may take 4 to 6 weeks for you to receive the cheque.
If you wish to discuss the matter you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
