Diatech Anchor Brakes....

I bought the diatech anchor front disk brake last July, and i have had nothing but trouble with it. The pistons/calipers, whatever, keep pushing the pads against the disc with such force that the bike is no longer rideable. Whenever i push them back to their original state, it's fine for the ride but when i next get the bike out, it's seized again. Has anyone got any recomendations as to what i could do. I bought them off Wiggle.co.uk if that's any help?