Unfair treatment and misinformation

I bought items using my paystrech account, the date for my next payment was 30th of April,then I used the paystrech account for the second time on the 25th of April then the dates on my app for my next payment changed from the 30th of April to the 31st of May, I was surprised when Finchoice called me and said I missed my payments and I'm in arrears, I asked how because my next payment is in May, they told me from their side the payment was already actioned, but my side the app doesn't show me anything, they said they will escalate the matter, but right now they are forcing me to pay the arrears and and the money that was due in April,and the amount keeps going up, on the 5th of May the total amount was R11330, on the 8th it went up to R12973 and right row it has gone up again to R13014.. Please help