Posted: Fri Mar 30, 2018 12:11pm
If you lived here more than 183 days a year, you were a fiscal resident. It's not something you can opt for, and you should have done a tax return for your first year of residence, whether or not tax was due.
If you still have a property here, and haven't been paying the annual non-resident tax, then that will almost certainly be the reason for the embargo by the tax office. If you no longer have property here then, as you say, you'll have to ask them.
Unfortunately, Agencia Tributaria don't publish email addresses, so it looks like you'll have to write to them and hope they reply. Guessing again, if they had a correct address for you, I'm sure they would have sent you details.