Hi... An owner should not hold back your deposit without reason, i refund my guests within 14 days but i do know owners that refund after 30 days and the reason is that owners get billed from the utilities monthly and if a guest has abused the villa as in run up a phone bill or used more power than normal an owner had a guest break the pool heater lock and turn on the pool heat then jam the lock back on when they finnished there stay, this showed up on monthly bill so the owner retained the excess charge for pool heat and new lock then sent the rest back.
If the owner does not respond reasonably then contact the website you found the villa on and report your concerns to the admin of the site.
Malcolm