Can anybody return the SIM cards to the companies if not in use?

First thing I want to tell you that you can't return any sim cards. No one will accept your sim cards.

And if you do not use sim cards for more than 6 months then you may loss your number means your sim card may get rejected.

So forgot about returning simcards and earning money. It's not at all possible.

How can you Use These Sim cards

You have 10 SIM cards. Each sim card has at least has 32K memory. Newer may have 64k or more. Means you can store 200 or more contacts per sim card. So you can use them as contact backup.

If you have 500 contacts in your phone , you can backup all your contacts in 2 or 3 sim cards.

Other thing is that if your number may be get rejected but still you can use your sim cards as memory device.

Hope you will get this.