Listing Issues Cant List new products

Is anyone else having problems listings items?

Im trying to add new products not yet sold on Amazon and everytime I try, I get one error or another. First it was telling me I didnt have my own brands permission to list! then it was telling me the GTIN conflicted with another of my items even though its an entirely different item with completely different identifiers, now it wont let me create any variations - as usual the support from AMZ is non-existent and they just keep sening me generic emails and telling me to use the upload spreadsheet instead of the tools in seller central but Im not sure how to do that.

Any advice or workarounds or recommendations of any tutorials on using the upload spreadsheet?

Thanks so much
Janine