cruise control mpg

[smartmpg]

Hi folks
To try and improve my MPG a decided to fit cruise control, see the siuation below....... who can help ?
I have just got my SMART 2009 451 Passion Coupe car back from the Merc dealer after it was there for 4 days whilst they tried to get cruise control working.
Before it went in I fitted the new control stalk supplied by SMART, I also fitted the cable supplied by SMART that goes between the wiper/cruise control switch to the SAM unit.
I put it in the Merc dealer have the TAN code updated on the Sam unit to enable the cruise control to function.
They got the TAN code from Merc headquarters in Germany ok for my VIN number car, but after 4 days of struggling they couldn’t get the car to accept the upgrade.
They said that although it is an upgrade they feel should be achievable, especially noting they got a TAN code for my car and it is sold as an extra with a new car, they cant find any 451 in the UK that has had this upgrade achieved.
So my question to you guys,…
1) Is this true?
2) Does anybody know of another 451 that has a proper Merc/SMART cruise control fitted as an extra after delivery ???
3) Does anybody know how to get it working ?