I have a flight from LHR-MUC in May which has arbitrarily (it appears) been cancelled.

I was travelling (as we do) when I got the email and thought as it's the best part of 4 months away so I'll wait a while before looking at my options and let the dust settle so to speak.

I'm sat at home due to the snow on the east coast and decide to look at this and find out that BA have rebooked me onto the later flight and I have not approved it, which completely scupper my plans and doest work for me as I will get in a lot later.
Now when I try to change online they want £400+.

I've probably done the wrong thing by being too patient but If I call do you think they will be able to change it without penalty?