Debt collector calling MY cell phone for my BROTHER?

This is strange. I got a call on my cell phone from a debt collector for my brother who is 10 years younger and hasn't lived in the same house with me since 1990. He lives in another state and has always had a different last name bec. he's my step-brother. HOW can a debt collection agency get my cell phone number and connect me with my brother? We don't even use the same cell phone carrier? We don't even really call each other except for holidays/birthdays bec. we're both busy. Can computer software REALLY track down your relative's cell phone numbers?