Did they say that updating your old bill validator was impossible? Did they offer or suggest a remedy, such as buying a bill validator from them? It may be difficult to find and buy a replacement bill validator that will accept Euro bills from a USA dealer. You could try contacting slot machine dealers and brokers that ship machines to countries outside the US, some of them may install bill validators compatible with Euro note usage.
Have you searched online for European-located slot machine dealers that have parts for sale?