So, it seems after many years of handy use one of the helpful user-made 2degrees chrome addons I was using for keeping an eye on cap (yes, some still keep one :P ) stopped working a couple of weeks back after they presumably changed the back-end interaction it had.

And guessing the maker as since realised, as the plugin has now been pulled from the store :(

Anyone else got the smarts that can whip one up. Once upon a time I used TUC (traffic usage checker) but pretty sure that has been abandoned now too.