I’m sorry to hear of the problems you have been having, and unfortunately I can’t offer any advice or consolation other than my (ex) 4 year old 1.6 TDCI Focus had exactly the same problem.
Like you I experienced numerous engine cuts when the weather was cold. Around freezing point the engine was fine, but at around -5 degrees centigrade it would cut out two or three times on a half hour journey, and at colder temperatures it was almost impossible to drive the car. The car was most likely to cut out when the demand for power was high, for example pulling away at junctions or joining fast moving traffic streams. Whilst the car was in warranty I took it back to the dealer numerous times, but to be honest the mechanics had no idea how to fix it and Ford didn’t want to know or help. Ford wouldn’t even talk to me unless I rang a premium rate number!!!!
I did get some advice that the problem can be caused by diesel fuel waxing in the fuel filter, and after getting the fuel filter changed the problem might have improved for a while but to be honest I don’t think it ever really fixed it. In the end, and once the car was out of warranty, I replaced it with an Audi (hopefully a more reliable make??) that runs on petrol (hopefully less to go wrong???).
The experience was very disappointing, and it was very annoying to have an unfixable car at only 30K on the clock. Buying the Focus proved to be a very costly mistake and I count myself lucky that at least I was in the fortunate position to have the cash to change to something else – but not everybody has. All in all, I’ve been very badly let down my Ford. The only positive thing I can say is that it was marvellous to get rid of the Focus and drive to work this week in temperatures of -8.5C without a single problem!
Best of luck.