They probably have a decal or sign for their alarm company near the front and/or back doors. Said decal/sign will have a phone number on it to call the alarm company. Call said number and tell them you need to contact the store's responsible party about a "problem" that you can't disclose.
If that doesn't work, leave the alarm company your number and ask them to forward it to the RP so they can call you directly.
Also try calling the cleaner's number and leaving a message.