Maybe try using indirect contact member approach - I believe that sometimes works when contact seller does not.
https://contact.ebay.com/ws/eBayISAPI.dll?FindAnswers&frm=284&requested=tomcat4000you need to replace your user ID in the above with that of the seller. And maybe try checking the "this is not about an item" box and then put the item number of the purchase in the text of your message instead to try to avoid the "contact seller" spinloop.
Might also want to try another browser - issues like this often only appear in one brand of browser. Old Firefox 31 is working working fine for me as we speak - just messaged one of my other accounts with no problem.