Early deductions of installments

I just convey my utter dissapointment in the service service of payjustnow. I purchased an item and as i understood it you have 3 months to pay. When i bought my item an immediate payment was deducted on 17 September which means my next payment was supposed to be 18 October. You demanded the next payment by 08 October. I paid interest on second installment . You then demanded 3rd payment by 1st november. I then paid it before i got charged interest again. From 17 september to 1 november is 6 and a half weeks . I thought this was a 3 month no interest payment plan .

This is bad service.