Right to license (minecraft) plugins without prior agreement?

My team and I have a problem right now, we bought a server network (discord rights, plugins, root access, domains etc) and we were not told until after the purchase that some plugins are licensed.
In our case there are 7 plugins that hold the name of the previous one
Server name should be bound.
We also took over the staff team from the server, as they also made a good impression when they got to know each other.
We were just surprised where their dev told us that the owner at that time only had the rights to license and that he (the dev below) owned the plugins.
(no idea if that matters, but the "owners" are settled in the US)

I find it quite questionable, because in such cases I always think of larger online businesses that you indicate a BEFORE you buy that you comply with the license agreement.

Now to the next point, who is right?
Do we now have the right to use the plugins in our name or are our hands really tied and have to continue working on the old server name?

Check out the license terms. It usually says who / what it applies to under what conditions and whether and how the license can be transferred.

If the existing license agreement is personal (in this case to the old owner) and is not transferable, you can no longer operate the software with this license.

But that we were not informed about the purchase until we paid? For me this is already fraudulent, we bought everything that belonged to the old owner and now we're not entitled to the plugins that we paid for?

Your business partner is the old owner, not the developer or anyone else.

It would only be a scam if the old owner knew about the problem and intentionally sold it incompletely, who does not own it or sells components that he was not allowed to sell.

What exactly was on sale? Must have been recorded somewhere: goods X for money Y.

Otherwise you have not received all of the goods and can usually. Insist on improvement. Or give the whole thing back.

It is like buying a functioning car, but where the exhaust is not included in the offer (which was not announced before the purchase) and is agreed upon by the old owner when it is handed over.

The best thing to do is get professional legal help.