Hello Alison,
Sorry to hear of your problems. As Trevor points out, this does not appear to be untypical after this recall, and I would think there isn't any doubt that the car is no longer what it was in terms of its performance - and I would anticipate, it's economy. Re, on one else has complained!? -well there are a couple on on this forum as I recall, and if it were mine I think I would be scanning the VW and Skoda forums and listing those who are discontent. Might be an idea to do this before ringing your contact.
I fear you may not get very far with this, but this may be rather pessimistic and let's hope I'm wrong, and you can get the sense you deserve.
If I'm right, it would be interesting to ask the question of simply returning the car's performance to what it originally was, and pointing out that if the car had been taken to the dealer for routine servicing and had been returned with a decreased performance then you would expect them to rectify whatever the fault was - reasonable question I think.
Final positive point - if all else fails, would it be possible to have the car mapped back to its original performance? Not my field, but perhaps Trevor and others could comment on this possibility.
Perhaps you could let us know how things pan out.
Kind regards,
Gareth.