Debit order taken ********

I have a personal loan at FNB. Monthly the payment is deducted via debit order. On the 2nd of July the deducted the payment from my account. Suddenly on Saturday the 9th of July FNB pusg through another debit order. The money in my account was for a Docters payment but now I can't pay the docter because FNB think they can take left right and center as it fits them. Try to call FNB but was holding on for so long that my cellphone run out of airtime. I m very ungry and desipointed in FNB. I had so many problems in the past with them that's why I have changed to another bank but I could not change the personalloan.