Debt collection has expiration date

I have recently been contacted by a debt collector about a very old debt that I wasn't aware still existed.

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In 2002, when my ex-husband and I split up, our previous marital home was repossessed by the bank. It was sold but there was still money owed because it was sold for less than the mortgage.

I made some payment arrangements at that time but then stopped making payments as I could no longer afford it. I received a few letters but the last one must be at least 15 years ago. I assumed the debt had either been written off or paid by my ex. I have now received a letter requesting I contact them about this account. Should I do this? Am I still liable for this debt after all this time?

There are 'prescription periods' - laws limiting time periods for recovering for debts - so they cannot be pursued indefinitely.