I cannot see the money returned to my checking account

I bought a laptop on Cyber Monday, but my debit card had an issue and couldn't complete the purchase, so I tried 2 more times, without success. When the issues with my debit card were solved, Dell charged me for the purchase of 3 laptops!!! And a Dell worker suggested me to cancel the 3 purchases, return the laptops and ask for a refund. I did, and in December 9th they assured me the money was posted for the 3 purchases and will be able to see it in my original mode of payment on my next billing statement, and they sent me the 3 credit memos to confirm the transaction . Today is January 4th and I still haven't seen any money returned to my checking account, I have called to the Store, but after putting many workers  on the phone, finally one of them said he couldn't do anything for me, and just provided me an email address to contact a specialist but the address doesn't exist, and finally didn't get any solution. I am surprised that I am not the only one with this problem, and I can't understand why Dell store confirms  that they refunded the money but finally it doesn't appear in the mode of payment. Really disappointed.