2 dubs Madras Presidency 1808

Hi, I bought this coin recently on eBay ( yes, no need to laugh) It looked genuine to me but when I had it in my hand a gut feeling made me doubt it's authenticity.It weighs only 8.8 gms and measures 34 mm and what looked like patina turned out to be dust that comes away with touch of a fine brush. Ay comments would be welcome. Thanks