If you're not seeing the Ambient Noise Control (ANC) page in the Melomania app, or you're unable to activate Active Noise Control using the touch controls on your A100 earbuds, it’s most likely because the earbuds are either still in their charging case or not being detected as worn.
These features will only appear and become available when the earbuds are out of the case and actively being worn. If the earbuds were still in the case when you checked, that would explain why ANC wasn’t visible — this is the intended behaviour.