Changing the gym visit cycle

I joined the gym in in September 2016. My cycle was counted from the 1st of October 2016 until the 30 of September 2017. I started of in visiting the gym quite frequently but unfortunately due to health issues I started slacking a bit, but I managed to achieve my 36 visits for the year starting 1st October 2016 until 30 September 2017. When I went onto my app I received a notice saying to keep my 75% discount I now need to visit the gym another 15 times by the 31st of October 2017 or I will be loosing my discount. I emailed Discovery Vitality and said to them that I do not understand why I now need to visit the gym another 15 times in a month and a half if I would like to keep my discount. They contacted me and started explaining to me that since I went to the gym in October 2016 15 and a few other reasons that I actually can't remember and that they say that this is all stipulated in my contract, but as far as I can remember it stipulates that you need to visit the gym 36 times in a rolling period of 12 months... which I did. My problem is not going to the gym another 15 times, my problem is why am I being told I need to visit the gym another 15 times before 31st October 2017 when I joined the gym beginning September 2016 and my 12 months started from the 1st of October 2016 until the 30th of September 2017?