Please Assist

I am currently banking with fnb account,what makes me angry is when we open bank accounts we are not informed everything in details.This week my parent deposited money for me to pay something important ,I did not withdraw the money because I knew I had to pay it Friday which is the 13th August. Today I open my banking app to buy airtime when I check my balance was low. I than did a chat with banking chat and spoke to a lady called Tintswalo I asked her about the money that went off in my account he informed me it was monthly charges, I asked her when does the monthly charges go off and who informed me that it goes off the 12th because I was under the impression that it deducts bank charges the last day of the month when my salary goes off she than disconnected the chat and I spoke to Dimakatso whom I also asked the same question that who informed me about the date that bank charges are suppose to go off my account and on the document that i signed when I opened the account is there something that specifies that she told me NO there is`nt the main thing she keeps repeating is I can change the date if I want to,Why inform me about changing the date if I was not notified or given an option to select a fee charges debit date? How am I going to pay for what I had to pay ? What frustrates me is each and every cent is budgeted for in this Pandemic there is no money. I am so angry !