I'd suggest sending email to the CEO (possibly using a temporary hotmail account set up for that in order to avoid any spam listing). But then this is just suggesting the obvious...
The only other thing I have to add is that providers seem to be abandoning their phones more quickly these days. Even a number of years ago this was happening with other companies like HTC and their HTC Desire model - after about a year it wasn't being supported any more. From Samsung's point of view the Note 3 is no longer the flagship phone - the Note 4 has taken that place.
Not that any of that excuses the responses of them that could easily be considered rude, but it might explain things at least since they appear to no longer consider it a handset worth supporting (at least if the responses you received are anything to go by).
In any case it might be worth avoiding them in future, especially since there are already rumours that the S7 might be released earlier than originally planned - this sort of planned obsolescence is only going to get worse for them if they increase the rate at which they release them.
Come to think of it: if it's a Note 3 then presumably it was bought within the last 2 years? Legally all such items bought within the EU have to have at least a 2 year warranty period (again IANAL). It might be worth threatening them with reporting them to Trading Standards since they would appear to have an obligation to either fix or replace it.