Unacceptable, this is theft

This morning an amount of R18868.29 was deducted from my account, with no prior warning from FNB. altough I am behind on my account it give FNB no right to deduct so much money from my account. My husband was retrenched making me the soul provided in my house, my car payments are behind, which i need to pay up to date this month to avoid repossession and I have to pay a very high electricity bill to avoid my electricity to be cut and FNB decided to be very selfish and deduct a substantial amount from my account and to have the nerve to send an sms afterwards to confirm they deduct this amount. I work in a call centre enviroment and can not answer my phone during the day. Please urgently pay my monies back into my account and negotiate an amount which is afordable. I have been in negitiations with other FNB departments to pay off my accounts, so i am not running away.