While at it, also how it grew 250 %.
Huh? I think you are confusing my post about £50 cash back with the Original Poster's contention that he had been 'robbed' of £20 cash back. He never did return to offer any further details regarding his alleged claim.
The amount of cash back was a limited time offer through a limited number of outlets including TomTom's own website of course which is how I bought mine. The amount of cash back varied with the particular model of TomTom on a sliding scale depending on how expensive the model was. My GO 6100 qualified for the maximum £50.
Personally I think these cashback offers are pretty cynical, and I'm not just referring to TomTom now. They hope that most customers will forget to claim in time or to claim at all. Then for those who do file a legitimate claim they hang on to the money until the very end (in my case somewhat beyond the end) of the stipulated repayment period.