I vaguely recall reading something, some time ago, that makes me think ABT was just an acronym for an automated payment system (Account Balance Transfer - or something similar).
If this is true in your case, then, as has already been suggested, your charges are probably down to some kind of repeat subscription & the reference to ABT may be the method of payment & not the payee.
Either way, as SUroot says, if your network provider can't help you to stop the payments, then a change of number would be the best option - being on PAYG it should be easy enough to pick up a free SIM.