Sellers not completing trade and I've accidently deleted feedback

Try not to stress too much about this. At least you have your money back. The store was honest in that regard. There are many reasons why they no longer have what you purchased. It got lost, (they go to get it in their warehouse after purchase & it's just not there) or they ran out of stock, someone listed in error. Or, with covid they could no longer get the stock?

You cannot do anything about deleted feedback, but, like I said before, they were honest enough to refund you. This has happened to me as well, I was glad to have my money back so I could look elsewhere for what I needed.

Ive bought a product on the 12th of November last year, its now the 27th of march, and the seller is not answering my messages and still has not sent my item. The item is worth over $500. I used afterpay and I have the bank account number of the seller. What can I do to get my money back?

I think this is way too long after the fact to be able to open a dispute via the usual methods which are only available for 45 days after purchase, so you should lodge a dispute manually by contacting Trademe. It says on the Afterpay website that the Merchant (Trademe) 

Merchant will help with:

Delivery

Returns

Refunds

Cancellations

The seller was actually manufacturing the item for me and he said it would take 60 days to fabricate. It seems that perhaps he knew what he was doing and possibly knew of certain loopholes in the trademe system. FYI this seller makes fibreglass parts for cars and there has been many people who have had the same experience as me. A seller like that is dangerous to trademe and I'm disappointed that the trademe administration hasnt picked up on him sooner

Is there no way to track down a auction you've Won go to pay but due to forgetting password to get in lost original TM Account.So unable to see winning auction or any details to make contact with seller. Searched Incase seller has relisted tried to get help through TM admin giving them as much detail including Username for auction but nothing has surfaced. I think screenshots are the only way one can stay on top of auctions win or lose. Pretty hopeless really TM needs to get up with technology.

Don't you have all the original emails when you bought? There will be an email saying you have won/bought, and in most cases a copy of the sellers payment instructions, although that will depend on how you purchased as TM don't email you that info every time. I do everything from my emails.

If going from the emails, or the listing number you don't need to be logged in or have an account to see the listing info, but you do have to log in to see payment instructions, or to pay online with Trademe if you wanted/needed to. Might pay to use Live Chat to contact Trademe to get your account sorted and reset.