Regarding this other chargeable work, i.e. the cams.
What did the original receipt for £360 say the bill was for?
IF it only itemised the mapping work and tax as totalling £360 then it would certainly be unfair for the trader to retrospectively apportion some of that amount to the mechanical work of tightening up the cams.
Having said that, I haven't seen the receipt which may well have been worded differently or in a less specific manner.
Regardless, it would appear that the trader is trying to blow smoke in our faces by turning the attention to the mechanical work. As Dude says, the £100 is not needed by CJ. To bring the conversation back to the original point, CJ expected the e-mamage to be correctly mapped by a reputable company who, it would appear, have failed in this task. None of us begrudge spending money on these cars, but we all expect to get some sort of value for what we do spend. The real question is 'Why were they unable to map the unit something close to correctly first time around?'
It is now up to this company to review their standards and perhaps dig a little deeper where the fine detail of the e-manage is concerned in order that they may keep the great reputation they have worked so hard to attain. It can be easy to become complacent, but when that happens, trouble usually follows.
Just swallow it and keep your good name. You probably don't need the £100 either.
Hope you get it sorted CJ.