Sharon Yon/ Debiting Clerk (Rude)

I've been with Zone Fitness for a while now and honestly for the price I'm paying I wasn't really expecting everything to be perfect and I'm not one to complain, but now I can't keep quiet. When I signed up on my contract it stated that I am to make payments on the 27th of each month or on the last day of each month which over been doing, however, I keep getting issues with their debits so I make manual payments only to keep getting told that I've not made payments or keep getting SMS's of demand to which I've expressed numerous times that this is off putting and a horrible customer experience. This morning I sent POP to the lady who deals with their debits Sharon Yon who is the most vile and rude person I've dealt with there. She's telling me that my payments need to be paid on the 25th and I've explained countless times to her that is what is stipulated on my contract, but instead she was rude and said that it was not her problem and will be revoking access. Someone from head office needs to call me or email me about this or I will take it further. I'm paying customer who knows their rights and so far my customer journey with this company has been the worst.