I have tried to correct the typos in the above message, but the edit function is not working. Aaaargh!
If someone is playing poker, he might say "I have won 10 dollars." Because he is still playing , it is possible that he will win more. If the game is over, he can still use the present perfect because the event is very recent and still present in the speaker's mind. But the s[peaker could also use the past tense because the game is over. This is an unfortunate overlap between the present perfect and the simple past and this overlap becaomesd the choice of the speaker. No grammar rule can determine exactly how recent an event must be for a speaker to use the present perfect.
In the case of your note, the event is recent enough to use the present perfect. One would not use it with reference to a test that was administered a year ago, but days to even weeks would be OK in this situation. The mere fact that the father is trying to get the score changed is evidence that the action is still in the writer's "present".
The overlap between past simple and present perfect is very difficult for learners. I dare say it is difficult even for native speakers. For example, a BrE speaker would be far more likely to use present perfect in many of these overlap situations than AmE speakers. Americans tend to use the simple past in many of these situations. Both choices can be correct.
Thanks for the wonderful explanation Mike. Now I can say that I know it.But I would also like you to rephrase the note.
Thanks again. You can't imagine how happy I am after understanding it.