If they are unsecured, then normal statute of limitations will apply, that is (I beleive) 5 years form last payment, if secured such as a mortgage, then the limitation is 15 years, if court ordered then indefinite.
There are recipricol arrangements for debt chasing with Portugal, but that will rely on there being some form of formal enforcement being authorised in Portugal first, either a Injunção or a Acção Declarativa. However, under Portugese law they cannot get a Injunção as you have not admitted the debt in writing to the court, so they would need a Acção Declarativa. These are expensive and unless there is a very good chance of financial return, they dont go for them.
You have said you have lived here since 2002, so I would think that if anything was goign to happen, it would have done so by now
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