Account credit never received or refunded to my original payment method

I cancelled my old plan on 03/21 but still got charged for the next billing cycle. Customer service informed me that I would receive a $29.03 account credit (going back to my original payment method) after returning the equipment. I returned it and now one month after the return I still havent got any refund, neither can I access billing info on my previous account. Where is my credit??