Is it possible to continue using a credit card when enrolled in a settlement plan?

Try not to use your credit card when you are already in a debt settlement process. It will give a negative impact to the creditors or collectors who have agreed to settle debts. However, you can use a card in an emergency. But make sure you repay the amount in full within time.

It is better not to use the card since you've already decided on an amount to repay to settle the card. Otherwise, there might be some problem in the contract or paying back the debt.
It is advisable that you don't start using your card, already settled, until your repay other cards. Even if you do so, then make sure that you repay the entire outstanding balance, or else, you may again have to experience debt problems.

No. You can't. The debt settlement company won't allow you to keep charging on the credit card. And you shouldn't also because you're already in debt. Pay in cash. Okay.

Not possible, your debt settlement company won't allow that.
It is because, if you keep increasing the due balance or should I say - the "debt amount" on that card, it'll be difficult for the settlement company to negotiate with the creditor/credit card company.

When you are trying to get out of debt, why will you swipe your card for additional debt? First, try to repay your existing debts. For the time being, practice a frugal life and save as much as you can. being debt free will help you focus on other financial aspects.
After you're out of debt, start managing your cards responsibly. That is, not to swipe your card for an amount that you can't repay within that billing cycle. Even if you need to buy an item, wait for the next billing cycle.