Not convinced?
Let me give you a more clear conception about it:
'Pre' and 'Pone' are suffixes. The rule and regulations which every language has, and so English has too, and the grammar says that suffix and prefix can only be added to a word that has its actual existence. Just for example, prenoon and postnoon. Here, noon has its existance in English. But, to make the word prepone and postpone, 'pone' word should first exist in English. Is there any word like 'pone' that we have heard while reading English? No, so how can we make these words avoiding all the complexities of grammar?
But I would like to remind you here, English is the language of exceptions. Although not accepted by British as well as American English, this word is fluently used by both the verses. Actually, these words are the inventions of Indians English. Our writers, poets, novelists have shown their great influence in the field of language and literature and that is why Indian English is so widely accepted all over the world.