Lost bag

In January of this year my sister had a birthday party. She booked a big house for all the visitors to fit in.Anywaythe day we left I forgot my bag in one of the bedroom cupboards.I was told the residence was a private residence but eventually security was sent to the house and the cleaner gave it to them. That was two weeks ago.Ive been calling and messaging them but I was sent from pillar to post.Even now I still haven't received my bag.