The balance of a credit card account is expected to be negative i.e. you owe the money. Hence when you buy products/services with the card it is expect to increase the negative balance. When you make payments is is expected to decrease the negative balance. If you were to have a positive balance in a credit card then the effect would be opposite, and it sounds like this is what is happening in your case.
Did you set an initial balance? Did you perhaps set it as a positive amount?