Can somebody please help me with UPC errors

I went to my local home department and saw they were having a sale on certain fall items so I bought about 4 items to test it out.

I get stuck as soon as I have to enter the products upc. Every single freaking time I try it says another product is associated with that upc. Ok cool, but it’s not even the same freaking product I’m trying to sell! Not even close to the same category is what’s making this confusing

So I go on google and search the upc and it’s the same exact item I have. I read somewhere products can have the same upc ( I don’t know if this is true) but if that’s the case why isn’t Amazon allowing it

Also if it isn’t true then why is that seller is able to use that upc but there not even selling the product that upc is for!!!!!! Amazon you’re not slick, because I was under the impression that upc numbers do I have to match the product title

I have no idea what to do, how on earth are other people able to go to stores and relist items for sale when you don’t even know if some other seller could be using that barcode to sell freaking honey buns and your product is for party decorations Doesn’t make sense to me

Also please don’t come for me I know I don’t know a lot about this but I’m still trying to figure this stuff out