A divorce decree does not protect you from joint debt. D did she forge your name to open this new credit? If so you can dispute it under fraud which would cause the creditors to produce something showing that you did indeed open the accounts. If these were joint accounts opened when you were still married or credit you co-signed for her you are, sad to say, on the hook for it.
If it is not your credit, the creditors and the bureaus alike my demand you take legal action which may land your loving ex in the pokey for credit card fraud. That being said, if she did forge your name on docs, she deserves no less