Hi Ajith22,
When an individual anomaly/issue occurs at a Test Center that implies that the testing environment was somehow unfair to an individual Test-taker, a formal investigation has to take place. That investigation can sometimes take several weeks before a resolution is reached (and until that time, no Official Score is issued). Assuming that your GMAT was administered without any problems (and since you received an Unofficial Score Report, I assume that everything was fine for you on Test Day), it's possible that there was an issue with someone else's Exam (someone who took the GMAT at the same time you did). It's also possible that there was a farther-reaching issue at that Center on that Day that impacted many Test-takers - meaning that all of the Scores issued that day have been held up. That type of situation would almost certainly require even more of an investigation, which would explain the delay in you receiving your Official Score.
Since it's now 1 month after you took your Exam, I would have expected some type of response by now. The most appropriate move for you at this point is probably to contact Customer Service again (and perhaps repeatedly) until you receive an appropriate response (re: your Official Score or the exact reason why it hasn't been issued yet).
GMAT assassins aren't born, they're made,
Rich