de*****ing client to sustain their business

i am not happy at all with standard bank. I feel like I am taken for granted and I am being *****ed by my own bank. I don't have an over draft on my account and I use the app a lot and SMS to check my balance. the last amount that I had on my account was R22 on the 23 of march 2021. A amount was sent to me of R1698.03 and current balance is R1163.80 so the amount that is missing in my account is R534.23. I had recently called standard bank and they told me that I had minus balance onto my account and which I do not understand because R2000 was sent to me and the balance was R2000 something and which I used that money and they said while that R2000 in my account I already had minus R300 and something. why did it not reflect on the app as R1700 since I owe R300 and why on the SMS notification its not saying I am on a minus as the application and the SMS balance are always the same. For example if I have R200 or R500 on my account and I spend the money that I know I have and when I receive money the say I am owing and they minus money from my account, Is this a trap for standard bank to make it look like your clients have money in their accounts and when they spend that money the client account goes to a minus without the clients knowledge and further charges occur from standard bank.