Hi Ollga, and sorry to hear about this - one year is a long time to solve a simple dispute. Now is the time to stop going around in circles and ask the protection of the LAWS of the Country which you are a resident of - SPAIN.
While lawsuit - technically is correct 🙂 it sounds big [as an archaic term] also is a little more complex for the problem you have; a lawsuit may have different claims, counter-claims, many people and cross claims; all you need is SMALL CLAIMS COURT.
In UK the sum is up to £5,000 in Spain is ~6.000 and depending if you are a' physical person' or a 'juridical one/ entity' you pay initial fee or 0.1 or 0.5% for claims over Euro 2,000. This is what will happen: (a) Airbnb will settle out-of-court [before case is heard] or(b) they might show up, in which case you get 'a clear win on the table' 3rd option is they fight it...but you have paper-work etc etc ++ include the time/ effort for each call/ endeavour you made so the sum totals - Euro 6,000 [go for the max] In this Juicio verbal you present yourself for sums <Euro <2,000 but more am not sure but one might need a lawyer.
Ask these people for advice Oficina de Atención al Ciudadano at the Juzgado on hows, wheres and whats - then get to work and take your money.