Chipping the EA 189 Engine

I have a 2010 1.6 diesel engined Fabia 2. I recently received a letter proposing I take the car to one of 3 local dealerships to have the 'improvements' developed by VW for this engine fitted/changed. Reading some of the threads here on this subject I am reluctant to do this. I have had the car for 6 years during which time several very small changes to the engine have resulted in 100+ miles of misery. Clouds of smoke, very poor running and stalling. The car gradually recovers but it takes a full tank of fuel (about 400 miles ) until it is back to normal.

However, the car now has 42,000 miles on it and performance is declining. Particularly its fuel consumption. In Winter this is rarely over 45 mpg and often around 40. In Summer this has climbed to the low 50's but this Summer it is still about 45 even on a good day. I live in mid-Norfolk so shopping trips are around 50 miles or more.

Now my question is has anyone had their car chipped, by whom and with what result? I am hoping to get the performance back to where it was with an equivalent improvement in fuel consumption. I don't drive a lot over a year (perhaps 6000 miles) but the increased fuel consumption is costing me a lot. Instead of the 6000 miles requiring 100 litres of fuel at 60 mpg. It needs 133 litres at 45. I am NOT looking for supercar performance. As I had hoped to keep the car most of its remaining life (another 12 years?) the cost of chipping and the better driving experience seem worth the money. But the question is where to get this.

By the way my local privately run garage which also does MOTs has advised me that a reputable chipping company should guarantee its work including an assurance that the work won't prevent it passing its MOT.

Any advice appreciated.