I have a department card but the stores all closed

Many store credit cards aren't run by the merchant. They use a company that does nothing but run store credit cards. When the store ceases to exist because of bankruptcy, or merger, or being bought by a competitor there should be plan for what to do with these accounts.

In some cases the accounts convert to being a generic credit card run by the same financial company. Though there is a chance that they are converted to being a Visa, MasterCard...

Of course if there is a merger of companies, or the company is bought by a competitor, there should still be a plan. Many times they are converted to store cards for the new company.

Go to the website where you pay your bills and see try and find out what the plan is. You might find that they have a deadline before they convert the accounts. They may decide it is worth lowering the rate or forgiving some debt if it allows them to close your account sooner. Because unless you have a reason to use the card at your formally favorite store which offered you perks, you are unlikely to use that card, and won't become a long time source of income.

Why would they WANT to give you a lower interest rate? After all, they are making $86 for every $100 you pay on the card. Pay off the card.

If you simply don't have the cash, you should be able to get a loan at a much lower interest rate, or find a balance transfer offer on a standard credit card. I get them regularly. Typically* there's a 3-4% fee, and a 12-18 month zero interest period.

*I have seen ones with no balance transfer fee, but not recently. Worth doing a search, though.