Hey @Dewizard21,
We have a bit more information about this situation in our Apex Coins article here, however the only situation where your Apex Coins will go into the negative is when you receive a refund or issue a chargeback for the payment method originally used to purchase those Apex Coins.
In that situation, the equivalent amount of Apex Coins will be removed from your account. If your account does not have a sufficient amount of Apex coins to cover this removal however, then your balance will go into the negative for the remaining amount.
Depending on when the refund/chargeback was received, there may be a processing period before the funds return to your bank account.
If you did not personally request a refund/chargeback, you may want to check with anyone else who uses your account or with the owner of the bank account used (if it is not you) in case they requested this.