Left earbud not charging

Hi,

Left earbud has stopped charging. When right pod is placed in charger it briefly flashes red, then flashes blue. It also flashes blue when opened.

Left bud does nothing, have managed to partially charge it for maybe a couple of hours but it does not switch on when the charger is opened, does not  flash red when placed in the charger, nothing.

I've tried cleaning the contacts but this is making no difference.