12 Months interest charged on a 6 months plan

I did not receive my statement since Aug 2020, recent statement received 11 Nov 2020 reflecting 6months plan and 12 months plan(with interest charged). I called to query why do I now have a 12 months plan on my statement which I never did for the past 5 years, Sino said I requested it on my Sep purchase , which I did not as the guy that was on the till did not pay attention when I told him to make it 6 months because he was busy chatting to a friend. Now Sino said unfortunately it cannot be reversed as its over 60 days but this is unfair because had I received my Sep statement I would have queried it then or Oct, they waited for 60 days to lapse then sent me a statement. I want all the interest charged in sep , oct and nov to be reversed as I have never requested a purchase for 12 months plan, this is just so unprofessional. Sino said I can call them again after 2 working days to follow up on the query but she doesn't promise that it will be reversed, so I must again call Truworths with my money to fix their mess, this is not on!!!!I need confirmation that it is reversed and a revised statement before COB today as I will be taking this to the media.