1. ."Out of 250 questions I have already finished 70 of them"
2. "I have already sent the required form but still din't get the call letter of it"
No, this needs to be either "but still haven't had the' or 'but didn't get the'. This part: 'the call letter of it' doesn't makes sense, what is a call letter? 'of it' isn't right either but until I know what a call letter is I can't help with that.
3. "From or Since moring I am reading this"
I have been reading this since this morning. (this means you were reading it this morning, it is now later in the day and you are still reading it. Is this the meaning you wanted?).