I think I would be sending an eBay message to the seller saying "What the h double hockey sticks are you talking about?"
And then ignore it.
If you are Blocked from bidding, and you need two Strikes for sellers to block you, then the seller is right that using another account to bid is not allowed.
If you have "only" one Strike, while a particular seller can specifically Block you, the automatic Block will not kick in.
Anything else is between the buyer and the seller. Nothing to do with you.