earlier/sooner

  1. Sorry I couldn’t write to you earlier, but I write now.
  2. Sorry I couldn’t write to you sooner, but I write now.
  3. Sorry for not writing sooner, but I write now.
    Please correct the above. Thanks.

‘I am writing now’ would be better in all the cases, Fathima.

Why even bother to say ‘but I am writing now’? It is pretty obvious that the person is writing, from the fact that the letter is received by the reader. It doesn’t add anything. Leave the phrase out and simplify the sentence by saying:

  1. Sorry I couldn’t write to you earlier.
  2. Sorry I couldn’t write to you sooner.
  3. Sorry for not writing sooner.

Do you tend to mean the way I have mentioned below? Please let me know.
Sorry, I couldn’t write to you earlier, but I am writing now. (not earlier than now)
Sorry, I couldn’t write to you earlier. (not earlier than I wrote)

Your questions don’t make sense.
The first implies that you are writing now, earlier than now.
The second implies that you wrote in the past being sorry that you couldn’t write earlier in the past.

It doesn’t matter how you try to explain it, the logic is that ‘I am writing now’ is not required as it is obvious from the fact that the letter, etc. exists.

It has made sense to the sensible already, whether the verbal is ‘write’ or ‘am writing’. My response ‘I am writing now’ would be better’ in place of ‘I write’ has taken a wrong direction.

Oh gosh, a reply. Such progress!
Pity about the first phrase.