I must be missing something, I think your position is just as illogical, inconsistent and inconvenient as the Revenue's.
You are being told very simply - pay by Debit Card any time up to the end of November or by SDA on 21 March.
But that’s exactly where the inconsistency is: one date for one method (which happens to be well before the tax is due), and a different date for another method!
Nothing else is like this. Consider a utility bill, for example. The bill for a particular month might say: "the amount is X and it is owed now, you have 30 days to pay, if paying by DD we’ll take it on day 20 of this (or whatever)."
Why can’t they be consistent (and fair, and convenient) and say exactly the same? "The tax is due on 1st Jan 2014, if paying by lump sum you have 3 months from that date in which to pay; if you have a DD, we’ll take it on 21st March. Your other option is to spread evenly over 12 months, but if you want to do this we need to know by end November 2013." How difficult can it be?
[Note: I’m aware that a significant part of the problem is the law they are working to in this case: we all know the track record of competence of our law makers.]