When did you purchase those credits?  Credit purchased are only valid for the current tax year.  Unused credits automatically expire at the end of each year.  Printing and filing of prior year returns used to be free but not any longer.  These have been the policy for some time already.

If you had purchased credits for TY2018 or earlier years, those had already expired.  Unless you have unused credits you bought for TY2019, you will see 0 as your balance on the account.

In case you do purchase additional credits, you need to make sure you trigger a print of each of the returns TODAY.  Otherwise, your account balance will join the new year countdown tonight and you can Auld Lang Syne to the credits you buy.

If you need to buy additional credits, I'd suggest that you wait until next year (aka tomorrow) unless you have a higher volume discount this year.