Left Powerbeats Pro buzzing and not connecting

I bought a pair of PowerBeats Pro over ear headphones 4 weeks ago from the Dixons Travel Shop at Heathrow Airport (which I understand has since closed down). They worked fine for 3 weeks but then the left one stopped charging. I managed to get it charging again but now, even though it says it has charged, it makes a buzzing noise as soon as I put them in my ears and it will not connect to the audio. The sound in the right ear is fine.

I have tried resetting, cleaning, connecting to a different device but they are still not working on the left side.

I dont know how I can return them (as the store has closed down) and I cant seem to find the right page on this site to get them replaced. Any ideas?