Question

I have not seen you since you failed in the examination.
correct
incorrect

Answer 1

Answer:

It is correct... for sure.....

Answer 2

Answer:

Completely correct

Explanation:

You can use 'haven't' in place of have not (if you want to) of not then 'have not' is also completely fine.

You can also add have after you, for example,

'I have not seen you since you have failed in the examination'