The question asks which statement is NOT correct. Qutub Minar was started by Qutubuddin Aibak, not Iltutmish. Iltutmish only added the next three stories to complete it. Therefore statement C is indeed the incorrect statement among the options. The other statements are historically accurate - Iltutmish did receive the caliph's investiture in 1228, he rightly refused to help Jalaluddin Mangbarni to protect his kingdom, and he is considered the true founder of the Delhi Sultanate.