Can't make or receive calls from iPhone 6s Plus

I strongly suggest you return it for a refund if you can.

If you can't, you can try putting it into recovery mode and restoring iOS using your computer. If it still won't work after that, and you can't get your money back, recycle it. It's not worth the potential cost of repair.

It's likely defective or possibly blacklisted as a stolen device.

What did your cellular carrier say when you reported the problem to them?

Was it working previously and it just stopped working, or has it ever worked for you on this phone?

Are you the original purchaser of the device or did you buy it second hand?