One word of Arabic could have more than one meanings. So besides meaning ‘final’, the word ‘khatam’ also means ‘the Seal’, as Qadianis proclaim. How will you disprove them using Quran alone?
From Qadiani website: Ahmadiyya Muslim Community
“He holds that the word Khatam denotes the consummation and completion of a thing, which he further explains by the words, authenticity, perfection and validity. When a seal is put to a letter it becomes authentic and complete. The seal may be put in the end or in the beginning. According to him, therefore, Khataman Nabiyyeen would mean the truest and the most perfect of prophets and not the last in point of time. It refers to his status and place among the prophets and not to the time of his advent.”
Looks like your whole religion is founded on number 19. A number which is based on a numerical system which was invented by Indians (not Arabs).