A Sennheiser marketing rep on Head-Fi won't be able to do a lot other than suggest contacting customer support.
If anyone has a genuine complaint about a Sennheiser product after pursuing all the other routes I'd suggest writing a strongly worded letter or email to one or all of these people.
As of January 1, 2023, the operational business of the Sennheiser Group will be managed by a team of six: The new Executive Management Board (EMB) includes Greg Beebe (Executive Vice President Professional Audio), Ron Holtdijk (Executive Vice President Business Communication), Ralf Oehl (CEO Georg Neumann GmbH), Steffen Heise (CFO), Dr. Andreas Fischer (COO) and Markus Redelstab (CTO). Peter Claussen and Thomas Weinzierl, who were previously COOs responsible for Professional Business and Supply Chain, will also remain on the EMB before their respective retirements in the course of the years 2023 and 2024. In the intervening period, they will gradually hand over their operational tasks and extensive knowledge to the new EMB. In the future, Co-CEOs Dr. Andreas and Daniel Sennheiser will primarily focus on corporate management and strategy development and devote more time to customers, while the other EMB members will manage the operational business. Yasmine Riechers and Mareike Oer complete the leadership of the Sennheiser Group as an extended management team, representing the Corporate Development Office and Brand & Corporate Communication.