Accelerator on ka getting stuck to the floor?

have recently purchased an old shape Ford Ka 2009 plate when you take the car out in the morning the accelerator sticks down and the car will rev up to 6000 revs, i took the car down to fords and they denied anything was wrong with it and just sprayed silicone spray down the throttle cable, but yet again i didnt even make a mile before it stuck again? anyone know how go get it fixed??