Thank you and apologies for the delay. I was not working yesterday. There is something about this matter that is not sitting right with me, so I have taken the last half hour to deeply look into this (you will not be charged for this time as I did it on my own time). I think this is a scam. Here is the reasoning for my thoughts.
They have not qualified the amount they have asked you to pay, they have just stated $2500.oo with no reason.
They have said that if you pay it they will reinstate your account, they do not have the power to do this, also, why would they allow you to keep selling something infringing on their trademark, does not make sense.
So I looked into this company. Firstly, very basic, GoDaddy page with spelling errors on it and very little information. I did try to call them but my phone will not let me call internationally I'm afraid. I looked at the staff member, they all seem to be qualified at a Supreme Court level but little else, as a lawyer I find that HIGHLY suspicious. Secondly there is little about these "attorneys" online and there are no pictures of them either.
The email is very short and provides absolutely no legal basis for their claim (you are reselling you did not make these). And finally the company they "claim" is their client ceased to exist in 1958 and is not Paramount Cartoon Studio so this company doesn't actually exist anymore apart from in the history books. Therefore, my advice is as follows.
Raise an official complaint to Etsy, state they are at fault and should be doing their due diligence in relation to these bogus law firm, as a result of suspending your account without doing due diligence, you have lost money and should be compensated. Etsy should be aware of this as I have found the same company sending various emails to Etsy users about the same thing, HIGHLY SUSPICIOUS that this same company would represent all the client's of people selling on Etsy. I think this is absolute bogus!