Selling unbranded products

My previous employer sold on amazon but has recently closed. I've decided to set up on my own selling the same things. I couldn't use their GTIN as the account has been closed so have paid GS1 to get my own GTIN numbers so as I could list on amazon. I will be personally making the products but they are not branded. I have tried listing the products on amazon but keep coming up with error codes 8572 which states my saying that my codes don't match the items I am trying to list. I've spoken to amazon help but this is proving really difficult . Can anyone help? TIA