Help! My tenants have a bat problem

[Mike Hourihan]

One of my rental condos has a small balcony and some bats have made it their home and are pooping all over the balcony and the tenants are complaining.   I called the condo office and asked them to send their maintenance guy to check it out and bill me.  Didn't hear anything for a couple weeks and now the tenants told me they had put something there to repel the bats but it didn't work.  I googled this and was going to try one of the common solutions which is hanging a sock with moth balls, but my tenant said she already tried that. Other repellants I've seen online are Phenol and peppermint oil.  There are people who trap and move them but that will probably have a higher cost and there are laws regarding that as well.  Trying to find an effective, legal, low cost method of getting them to go away.  Looking for suggestions based on ACTUAL EXPERIENCE.  I can google myself, so please don't suggest anything you've only read about online. Thanks!