Hello Asimali,
First of all I strongly advise you not to pay a single penny to an agent because in todays world of internet, and education there is no information you can not access directly.
Secondly, the only certification accepted by the German High Commission is the exam conducted by the Goethe Institute.
Thirdly, a lot of Pakistanis were misusing the subsidized education system of Germany and instead of genuine students, agents were sending planes full of fake students who end up as beggars on German streets and cause disgrace to our nation.
As a solution, the German High Commission was advised to put a filter system and since January 2014, any student proceeding to Germany on a student visa, in addition to demonstrating competence in German language, will be required to deposit a sum of approx Rs. 16 Lacs in Euros in a German bank.
I suggest you look at the complete picture before making the most important decision in your life. 