If the bank is not happy with the CO card being used for coin purchase, it would close the CO credit card, not the personal checking. Remember, this is a personal checking account, not a CO checking account. It just have a fee-based CO branded debit card that allows you to earn miles with non-PIN transactions. You can switch the CO debit card back to a no fee regular debit card anytime you want, and it does not affect the nature of the checking account.

They will close the checking account with the pattern of money immediately withdrawn after coins deposits, regardless how the coins are obtained.

Read that the poster got a call from the Compliance Dept - said Dept has the responsibilities to make sure the bank follows all the government rules and regulations. In this case, the activities of OP's checking account have all the look of money laundering even though it is not. The bank needs to report such activities for government investigation. This means more work to the bank that has to be done on an already unprofitable account. It is an easy decision to simply close the account because bank has the right to close any account which it deems is not for the "intended purpose".

You have to understand that the bank is a for profit business. This is a business decision to close unprofitable account that has questionable activities.

Now the lingering question is, since the account is closed less than 6 months, would the OP still keep the bonus miles?