Elrog 300B vs Takatsuki 300B tubes

I got a pair of ER300B from TrueAudiophile in March 2015. One of tubes has failed in June 2015. As per TrueAudiophile request I shipped tubes directly to the factory.
Here is from the email from TrueAudiophile regarding conversation with the factory:
... I went over it very calmly with him explaining he needs to honor the warranty. He refused. He then hung up on me....
I also email to Elrog stating tubes S/N, date of purches etc. No reply.

As somewhat of an outsider, but one who is interested since I own an 300b SET, I am concerned by the number of failures and, even more, by the inconsistency in the company's response. Elrog has to understand that in the age of the Internet, all of this becomes common knowledge.

Matthias, Thanks for the PM. I responded with the information you requested.

If Elrog has figured out the cause of the reliability issue causing premature tube failure this will be wonderful news for music lovers. I spent the weekend doing quite a bit of listening using the replacement Elrogs(what a pleasure it was). This is a special tube and contributes to superb music reproduction, really involving. Man, I sincerely hope that Elrog gets it all corrected, what a beautiful sounding tube it is. Come on you engineers!

Mathias,
I emailed Elrog multiple times regarding my tubes, got no reply.
Here it is again:
Serial numbers: 09471 and 09505.
Tubes have arrived to Elrog on 20.06.2015 11:00

Tubes were used in AN amplifier, cathode bias 900 Ohm,
HT 425V, 5.0v DC regulated heaters PS.

Tube failed during listening, there is no issue with the emission or heater, tube just turned into diode.

You respond is appreciated.