The way we handle security deposits is by placing a "hold" on your account for the amount of the security deposit. When that happens, your bank creates a pending transaction but never actually processes that payment to transfer the money to us.
Due to the fact that you were never actually charged that money, you are not going to see a refund in your account. Instead, that original pending transaction will either say it was voided, or it will have disappeared altogether.
If you have already received an email stating that your security deposit has been released back to you, please keep in mind that it can take anywhere from a few business days to several weeks for your financial institution to release the funds back onto your card. If you still do not see them, we suggest reaching out to your credit card company to have them look into it on their end.