I ordered a 20000mah PowerBank, they delivered on time but didn't deliver exactly what I purchased

I ordered a 20000mah PowerBank, they delivered on time but didn't deliver exactly what I purchased. I got a 12000mah PowerBank but the box is written 20000mah... and the PowerBank is not the same as the one I picked, it doesn't fully charge my phone.. it doesn't last more than 2 hours. I'm disappointed.