I can't believe he left only the house.
Furniture, clothing, books, collectibles, tools, car, electrical goods, everything - all form part of the estate - everything he owned.
As sole executor you are legally responsible to ensure the debts are paid. And please don't try the 'not known at this address' - the credit card company will know he owned his home and will dig deeper.
TALK to the credit card company, explain the situation and try and come to an arrangement, if you are not prepared to sell the assets to pay the debt (as you are legally obliged to do)