bought one from amazon a year ago, didn't use it much, when i do use it, I feel its noise cancellation is not on par with my QC15. I found in many instances my 15 just out-perform 25 in noise cancellation.
Welcome to the community, I am sorry to hear that the noise cancellation of your QC25 headphones appears to no longer be working.
I would love to offer some troubleshooting for this.
I'd firstly suggest that you ensure that the earcups are tightly seated against the head and that these are securely attached to the earcup. Secondly, please ensure that the headphone openings are clean and free of debris.
I hope this helps. However, if you are still experiencing issues after testing this troubleshooting, please reach out to your local service team for further assistance. Our local support team can be contacted via clicking this link and selecting your region, this will redirect you to our website. Please scroll to the bottom of the website and there you will find a 'Contact Us' tab, this will provide you with all the relevant contact information for your country.