So dissapointed with PayJoy

Im so shocked at my balance for a cellphone purchase with PayJoy at Mr Price cellular in Phoenix. about a week ago i assisted by a lady at the store because i wanted to buy a phone so the lady told me about PayJoy the next day my husband went back to the store a first he said they had made wait so long for the processing of the application then when they approved he asked if he could make monthly payments instead of weekly but they told him heneeded to make his first payment. On that day he had made a 30% deposit towards(R3299) whch is required so he payed R900 so it approved PayJoy and the app gave next payment date which is 7days aftr the purchase on the slip the PayJoy payment reflected R2474 only to find out that ther was an intrestd added by PayJoy when i checked on the app saying i owe R6327. 79 almost double the amount of the phone price. So i went to the store to make my first week payment of R162 nd i asked abt the amount reflecting on the app nd the assistant told me its intrest and they know nothing about it because payjoy charges intrest and they dont know how its calculated ive tried cantacting them but no luck. Im getting constant reminders from the app to make my next weekly payment or my phone will be blocked if i dnt make payment. Im so dissapointed if only i knew i would have just got the phone on cash bases but the way the assistant explained the payment plan it sounded so tempting that i could purchase a smartphone nd make easy payements