there is what it's called egyptien arabic and standard arabic i advise you to learn standard arabic

The Arabic dialects even the classical ones use to simplify the 'hamza' to its alternative vowel (closest in sound or part of its radical ...). for example رَأْس ← راس ؛ الأَرْض ← الارْض شُؤْم ← شوم ؛ مُؤَنَّث ← مُوَنَّث ذِئْب ← ذيب ؛ بِئْر ← بير؛ نائِم ← نايِم In the same way, you may find some variants like مِئَة ← مِية ...; But not in the standard books, so it could be just a mistake (ي - ئ). Concerning the alif of 'مائة', it has historical reasons in orthography.

good question . there is different points of view in correct way to write this word . some group say مئة and other مائة Pronunciation: these words have one way is (مئة ) even if u write مائة :)