If your problems are anything to do with the item you sold, are you registered to sell and signed up for managed payments ?

https://www.ebay.com.au/help/selling/getting-paid/registering-seller?id=4792&srsltid=AfmBOoqLCWh6IvmjA2RyF7wLlw7n4DItY_RtRE0M5blwCHPVy3od5nEx

Payment holds  of 14-30 days apply  for new and infrequent sellers in which case your hold should soon end. 

Have a look at the payments tab in your seller hub

https://www.ebay.com.au/help/selling/getting-paid/getting-paid-items-youve-sold/transaction-holds?id=4816&srsltid=AfmBOooc10tb3IRte5jOsG4b5UzKzDAIwAa9atvncUeQpRgGugzx25pK

If the buyer didn't pay , an unpaid item case can only be opened  for up to 30 days after the sale

eBay Help is at the top of every page, type speak to an agent in the chatbot during business hours

Or you can ask other members here, we actually know what we are talking about, know eBay policies and have experience as sellers and buyers (none of which eBay staff, who type from a script have)

If you have issues with transactions as a seller, you need to open the appropriate dispute and follow through with it, within the time limit

The two sellers that you have left negs for, one of them beyond awful feedback, the other clearly drop shipping knock off garage (including death trap, non compliant batteries . Those are things easily avoided by not supporting such sellers

If you buy from those sorts of sellers, issues are to be expected

emails are pointless, they are not read by humans and any replies are copy and paste/bot automated