Sennheiser Warranty Problem - Malfunctioning Momentum Tws 3  Earbuds, 18 Days No Fix

The Sennheiser Bluetooth headphones I purchased from Media Markt are not working properly, even after trying to reconfigure them 2-3 times. They worked on and off for a bit, but then one of the earbuds malfunctioned again. I took them to Media Markt for servicing and asked for a replacement covered by the warranty. Even though it's been 18 days and I was promised updates, I haven't heard anything through SMS, phone, or email. I am dissatisfied with both Media Markt and the Sennheiser manufacturer and importer.