Sorry this happened to you, julerz.
Unfortunately, this incident negatively affect your reputation and harm your business as a campaign manager.
You acted as escrow so it doesn't matter whether you are telling the truth or not (I believe you are), it was your duty to keep the coins safe.

Right now, the best/right thing to do is to find a way to refund the missing amount from your own pocket then find out what happened and who got access to your wallet/device.