I found a bug in a multi-million teleco's mobile money service. They have this auto-debit option where an amount (specified by the customer) is periodically deducted from the customer's account. Instead the system debits the customers account with the said amount (transaction reversal) whenever it tries to to auto-debit but the customer does not have enable balance (up to the specified amount).

So assuming you set monthly auto-debit to $1000 but you had only $100 dollars in your account. The system debits (via a transaction reversal) your account with $1000 (because deducting $1000 dollars will results in transaction failure since you don't have enough balance).

After reporting this bug, my account is totally closed. I called their customer care and I was told to go to their customer care center (which is hours of drive away from where is live). The unfortunate this is that all the money I have is locked up in the account.