Return Iphone to buy a discounted version of that iphone

Hey, I want to ask about the refund policy. If i want to return iphone 8 plus because it is getting a discount, can i get a full refund then buy the iphone 8 plus again. I bought my iphone 8 plus for about 870 dollars then will my refund be 870 dollars even though the iphone is worth less after discount. What are the requirements for returning an iphone? If I used my iphone after I bought it, i downloaded apps,can i still return it within 14 days of purchase. And i bought the phone in cash can i get cash back. I dont have a debit or credit card yet so how will apple refund me if by mailing a check. If by giftcard, i will have money left over from buying the discounted iphone 8 and i will be forced to use the remaining money for apple products.