One, I didn’t call them as I don’t them. Next, most likely spoofed call using my phone number. Either a robo-call, or possibly a bill collector. Had a robo-call using my own phone number a while back. Didn’t answer as it was using the same phone number it was calling me on.
I get so many spoofed calls, probably 95% fall in this category. I use Zedge with an annoying ring tone for unknown callers. The small handful of people who call me, I choose one of several ringtones I can hear and assign it to those numbers. Most people use Facebook or other social media to contact me.
The only time I use one phone to call the other phone is when I am trying to figure the location of the other phone.
Spoofing a number isn’t legal if you plan on scamming someone, defrauding them, causing harm, or wrongfully obtaining something of value. The TRACE Act was signed in 2019 to address many of the issues. Including options to block most spoofed calls without being charged extra by your phone company.
Canada allows spoofed calls, but has tried to address the issue several times. The current deadline is June 2021 although they are creating it as a mandate since it has moved back so many times.
Both Canada and the U. S. are looking at STIR/SHAKEN as a solution: https://www.fcc.gov/consumers/guides/spoofing-and-caller-id is the FCC guide to spoofing and Caller ID. It has some great advice on what to do and not do.
India has a tougher policy on it with fines and/or possible jail time involved. No word on how big the fines can be.
The United Kingdom appears to have a very tough policy as a company can be fined £2 million for violating it.