Charm person and why did this happen?


Hello i am fairly new to DnD however i have years of roleplay experience. Last night i attempted to charm a shopkeep old lady and the dm didn’t tell me iff i was successfull or failed he seems to do this with everything. Anyway having read the description of charm person and then reading several views on it by others it seems the common consensus if the nps pass’s the save and is not charmed that nothing should happen however what happened is this. The dm toled me the lady’s eyes started to glow slightly and to tell her what to do and so i asked her to give me some potions. I understood it as though if her eyes changed then yes she was charmed apparently this was not the case and she pulled a crossbow out on me instead so i left the shop. I really think i’ve been cheated here but i want your guys opinions as i’m unsure wether i need to talk to the gm or not like i said the common consensus i found is that if an npc is not charmed then nothing at all should happen untill the spell ends which is says they know they are charmed but they have to have been charmed in the first place to know this.