I actually had to change my phone number due to something similar. The last 7 digits of my phone number was the first 7 digits of the spammer's area code + number. So when people called back the missed number from a landline (for those that don't remember, the local area code was implied when using a landline phone), it would call me. Eg:

1. landline user sees missed call from (123) 456-7890, ie: the spammer
2. landline returns call to (local area code) 123-4567, ie: me
3. people calling me all day and asking why i called them
4. voice mail box full of confused boomers.
5. 700 precious shared family minutes decimated (for those that don't remember, you used to have minute limits for your cell phone plan and would get charged exorbitant rates for going over) and lectures from my dad about responsibility