Does it charge OK via PC/laptop ?

If so, then your charger's duff, sling it back - although if lead and plug are seperate, try another cable, that you know works on whatever it came with (any with the right plug will do, except anything Apple.) If it still doesn't work, the charger body/plug bit is definitely dud.

If it doesn't charge via PC/laptop, it sounds like a faulty battery, Sale of Goods Act on your supplier, replacement unit please.

You sadly can't (easily) change battery yourself.