Debit orders from my account

Good day recently I noticed debit orders on my banking statement the I was unaware of. I contacted the company and told them I did not accept any of their services they however refunded me back in this month for all the monies they debited. Today I went to my bank statement and see they made another debit from my account of R99.99. I am wondering how these companies get our banking details and have authority to run a debit without the us knowing. I am really concerned as this is happening for a few months. This has to stop as I am not in the position to keep calling them for a refund .