How did collection agency get my phone number?

[Thomas V]

I have been sending in my mothers bills not because I want to but she wants me to. She was rushed to a hospital by ambulance a few months ago. I sent in insurance information and thought everything was covered. The mileage cost of over $100 was not covered. My mom wrote me a note to call this number and to pay my bills. She must have got this call from her home phone and I noticed that I got a message from them on my cell phone. I only have my cell phone number for about a month and gave the phone number just to my mom. Since nobody knows my phone number I don't know how I got this message. It really isn't even my bill it is my mothers. I think since I handle her bills she must have told them my phone number. How do you feel this collection agency got my phone number?