I also feel very, very sorry for you. We had EXACTLY the same problem, but British Gas took reponsibility as they had installed the boiler, although that was several years ago.
The engineer told hubby that they have suddenly had loads of problems with the condensation pipes freezing up as the weather has been so much colder this winter.
With a lot of pestering we were able to get it sorted before this latest lot of snow and ice - we were very lucky.
I'll keep my fingers crossed that you are also able to to get the situation rectified as soon as possible. I'm sure that many people who have had a new condensating boiler installed in the last few years will encounter this problem because of the severity of the weather - I don't think anyone anticipated this happening.
Wishing you all the best - do keep us posted.