The followers of Mirza Ghulam Ahmad of Qadian are Qadiani whether they belong to the Qadiani jamaat of Rabwah or the Lahori jamaat of Qadianis. But they call themselves "Ahmadi" pleading that Mirza Ghulam Ahmad befits the verse "Asmahu Ahmad" in the holy Quran whereas according to the muslims this quranic verse relates to the holy prophet Muhammad (SAW).
Taking undue advantage of the word, Ahmad in his name Mirza Ghulam Ahmad twisted the meaning of the above verse in his favour and claimed prophethood on this basis, though his name actually means, "slave of Ahmad". According to the Holy Quran both Ahmad and Muhammad are the holy name of our Prophet (SAW)
Therefore, the application of the said Quranic verse to Mirza Ghulam Ahmad of Qadian is a deliberate alteration of the Holy Quran. On this basis calling Qadianis as Ahmadis is "harram" (forbidden) and unlawful.