The seller you mention sells a huge range of items and sells multiple lots every day.
You bought two lots from them and didn't pay.
After 4 days, the seller cancelled the sales using the reason 'buyer did not pay'. Because they are such a big seller, I would guess they have their account set up to automatically cancel in this way when buyers do not pay within 4 days. Such a big seller would not be able to monitor sales and cancel individual items when the buyer didn't pay.
You now have two unpaid item strikes on your account.
These will last a year and cannot be cancelled.
You will find that a lot of sellers will automatically block bids from you because you now have two unpaid item strikes.
You could message this particular seller and ask them if they can put you on their exemption list so you can buy from them again but they do not have to agree.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)