Emergency after hours phone number

How do you handle emergencies that happen after your office is closed? I thought the call center (Open Tech) was supposed to call the onsite manager if a customer has an emergency. My office closes at 5PM, the facility closes at 9PM. Our company does not supply us with a cell phone or phone number for emergencies. I am currently compiling research to prove we do in fact need a company phone. I have reached out to Open Tech with a request on how they handle after hours calls for us, pertaining to emergencies, waiting for their response. I am getting voicemails from irate customers that have true issues, but the voicemail goes to my office only, so I am only getting them when I come in in the morning, well after the customer has had a stressful experience. I previously had a google number that would ring my cell for after hour emergencies, unfortunately my customers would call it during the day, and honestly I don't want/need to be using my personal phone.
What are my options?