Unauthorized NAEDO debit order

I have been experiencing an unauthorized debit order on my account,it has been a matter of 4-5 months now everytime on the 15th of each month money gets deducted from my account that I do not know what im paying for..sometimes its R200,sometimes its a R100 even today they just deducted R89 and recently money just goes missing from my account...the debit is a NAEDO FNASERV which I do not know what that is and its been happening for months.. I have been with ABSA since I was 10 years of age,this is really disheartening,im very frustrated because sometimes they take the only money I have to survive as I am a student..I feel this is very unfair and I'd really like to know what is going on,im really considering changing banks as I feel these are ********** activities..