Help required in returning mobile on Amazon

Not possible unless there’s a defect in it
Unlike Fashion/Home & Kitchen category, etc. you can’t try and buy mobiles

olx pe try karo bechne same price with bill dont open box seal

You should have cancelled the order before it was delivered. Write a mail to Amazon & see if they can help. You may also sell your phone on olx with a reduced price

Talk to support
Some are very generous, they can open a return/replacement request w/o any engineer visit

best way is contacting amazon and explain them u ordered it by mistake and also tell box is sealed, but very little chance they will help u. 

otherwise sell it at shop nearby where 2nd hand phones are sold & purchased.