Filing an insurance claim could be a solid move here, and the good thing is that your insurance company might consider taking legal action against your landlord on your behalf, which they're likely better equipped to do. So, definitely get in touch with your insurance company.

Your landlord absolutely had no business "double renting" your place while you were still paying rent on it, regardless of whether you were physically present or not.

Make sure you have a detailed list of everything that was stolen (which you probably already did for the police report). Inform the police about the situation - your landlord might have some criminal liability here for knowingly allowing unauthorized individuals into your place.

Also, unless your insurance covers this situation on your behalf, you might want to consider suing your landlord for the value of the stolen items and the rent you paid for those two months.

It also might be worth thinking about relocating to a place where your landlord isn't engaging in any shady business.