Serial number and IMEI on the box are different than the Phone's

I bought a brand new Iphone X before a couple of months from an online store called NOON. Its a well known store in the middle east. After using the Iphone X for a couple of months I discovered that the serial number and the IMEI on the box are different than the Iphone's. I looked them up on the internet I found out that the serial number on the box is an iphone 7 plus serial number, the IMEI is a samsung phone IMEI but the ones in the phone are correct, they belong to the same Iphone X. Could they be selling used Iphones as new ones? because the performance of the phone is bad. It lags a lot. And it turns off once it reaches 10%. also, on the back of the box it says that there is a lightning to headphone jack adaptor but I can not find it there is nothing like that inside of the box. Can you please guide me through my problem? what should I do ?

Thanks.

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