Didn't or Haven't (How are you getting on? I am sorry I didn't reply for your...)

[Ganesh]

Dear Teacher

I am writing to my friend as follows:

How are you getting on? I am sorry I didn't reply for your letter early
or
How are you getting on? I am sorry I haven't reply for your letter early

Which one of the above is correct

Many thanks
Ganesh

[Mister Micawber]

.
Both of these are correct:

How are you getting on? I am sorry I didn't reply to your letter earlier.
How are you getting on? I am sorry I haven't replied to your letter before now.
.
_________________
Native English teacher at Mister Micawber's

[Sureshvemuri]

Mister Micawber:

Do these sentences make sense?

I haven't known about this before now = Just now, I know this.

I did not know till now = Now also I don't know about this.

Thanks,
Suresh

[Mister Micawber]

.
The meanings are the same. The present perfect does not work in your first sentence, since the time phrase 'before now' sets the action of knowing firmly in the completed past.

I didn't know about this before now = Just now, I know this.
I did not know till now = Just now, I know this.
_________________
Native English teacher at Mister Micawber's

[Sureshvemuri]

[Mister Micawber]

.
I still haven't (received/got/gotten) that (file/information).
I haven't (received/got/gotten) that (file/information) yet.
.
_________________
Native English teacher at Mister Micawber's

[Sureshvemuri]