Telkom has bad service (I think they don't even train their stuff)

I went to cancel my contract with them since I'm done paying and the guy I found at the shop said I should have came sameday they debited their last amount so because I came on the 1st of instead of the 30th they can't immediately cancel my contract meaning they're going to bill full amount again, I ask how because if it's like that then bill your data amount alone and live the cell phone why am I continuing paying for the phone too, the guy tells me it's a procedure there's nothing he can do