Using API is an advantage, not spam tool, if you have indeed that much items, make some time, list all of them at once and wait. Sell your items all of them, then re-stock. What about people who started selling recently, they can’t be seen because of you ? Gameflip is an amazing market with great prices and sellers but constantly spamming isn’t good 
. I dont know if your suspension is permanent but wait for Gameflip support to reply.
Regards