ACCOUNT BILLING AND BAD ATTITUDE OF STAFF

I took a contract with intellicell in November 2015 a ZTE phone. i signed an agreement of the debit order to be deducted on 25th of each month as i am getting paid on this day. But Intellicell do not stick to our agreement they deduct on their own dates as long as my account have the money.on the 18 February 2016 Intellicell debited R299 again on my account. i tried calling their customer service dpt and i was assisted by Shane.When i ask her why is Intellicel deducting on my account on any day they decide to deduct but not an agreement date of which is the 25th of each month. Shane told me she doesnt have any idea as to why intellicel deduct during the month. Then i requested her to transfer my query to the manager to assist me since she said she doesnt know why sudden deduction are happening into my account she said she is not been able to transfer calls but she will instruct finance department people to contact me and no1 contacted me as she promised. i requested her to give me her name and surname but she refused to give me her surname. im so disapointed by her service. i stil need an answer from intellicel as to why they deduct at any time not accoriding to our aggreement