Thanks for sharing. Really interesting.
So it seems that, in the Canaries at least, the time they take to refund the retention is July 2013 > Oct 2015 = 2 years and 3 months, or at least in your case. That’s a scandal.
It’s also a scandal that they did not notify you, or provide you with any further information. You should have received an official letter from the tax office explaining the amount returned. Have you really heard nothing from the tax office?
If you sold at a loss, and the 3% is there to cover capital gains, you should have received a full refund. I’ll ask a tax lawyer about this.