Sony PlayStation DualSense/Authorized Service Complaint

I had bought a PlayStation 5 and an extra DualSense controller as a backup from a technology store. The controller that came with the PlayStation had some issues from the first day, such as sticking buttons and failure to register commands, but since I didn't use those buttons in the games I played, I didn't worry about it. Last week, a new game I started required me to actively use those buttons, so I took out the backup controller from the box and started playing. The other buttons on this backup controller were working fine, but I could sense something strange when I pressed the X and those buttons, although they didn't hinder me from playing the game. Two days after I started using the controller from the box, I went on a holiday for Eid. When I returned and started using the controller, I noticed that the X and those buttons were getting stuck when pressed. They didn't spring back out. Since it was under warranty, I left it at Mekel Elektronik, the authorized service center for Sony in Beşiktaş Fulya. Today, they called me and said that they would evaluate the device as out of warranty due to liquid damage and provide a paid service. I used the controller for only 2 days, and before going on vacation, I placed it in a location where liquid contact was not possible, on its own charging stand. I can't prove that there was no liquid contact, so I can't convince the authorized service center. They are saying that if you want, you can come and take your device; there's nothing else we can do. Authorized service centers need to stop using the excuse of liquid damage. I've encountered this issue with other companies as well. The only possible reason could be that there might have been liquid contact due to sweaty hands, but aren't these devices meant to be held in hands while being used? Especially in the summer months, isn't it quite normal for hands to sweat? If no precautions were taken during the manufacturing process, the responsibility lies with the manufacturer, not the customer. Therefore, I demand that my controller be repaired under warranty.