Opticians - please can you advise me...?

I got my contact lenses from Specsavers today but the prescription numbers on the paperwork in the box are different to the prescriptions numbers on my eye test for spectacles, when I had my eyes tested in May. (i.e. power, BC, Cyl and Axis are all different). When I rang Specsavers they said that it's supposed to be different as the lenses are closer to the eye than the spectacles. Is this true? Are they ripping me off? Have I got the right thing?