Agree customer

I would like to lay a complain about RCS including my jet account.so i went to pay my account on the 27 of feb but i paid it at there FIX clothing store.the cashier didnt mind me paying without my card as i had my ID with me.2 weeks later yesterday i recieve a rude phone call from 1 of there consultants threathening that i would be blacklisted yet thou its a huge amount i owe i pay my installments every single month without fail.apparently they cannot track the payment i dont understand howcome im so disgusted with them something needs to be done