False advertising

I had an Andowl 40000mah powerbank for a while now had it in my cupboard This morning the batteries swelled up and the cover.came of.Only to.disvover that inside there are only 3 x. 10000 batteries.On the cover says 40000 and that is what i paid for .This is ansolutely daylight ******* who can i speak to.concerningl.this issue