It is for life, perpetuity.
Its bad news I am afraid.
You are not the first person and will not be the last person to ask about these scheme here.
But the sad fact is that under Timeshare Regulations you had a limited time to cancel the contract.
As you did not and it has been several years then sadly you are liable for the fees each year and every year for life.
You could potentially sue for breach of contract and you have 6 years from the date of breach to do this - but given the value I and what is contained within the contract you may have to sue in Portugal -
Indeed an hurdle you face is that you have waited 'years' you may have difficulty explaining why you waited so long.
I am sorry if this is not the answer you are after and certainly not the one I want to give you, but I have a duty to be honest.
We are asked lots on here about these schemes and sadly the answer is the same.
Can I clarify anything for you about this today please?