Bas call centre service

Every month I have a fixed amount I pay over to Russells but some months I pay more then the fixed amount, when I have the money. This month however I cannot afford to pay the full amount and have spoken to the call centre countless times and even made an arrangement with the person in the call centre to pay a lesser amount this month. Now a lady from the call centre has already phoned me 3 times today to ask for more money. Even though i told her i have an arrangement to pay less this month she keeps phoning back to ask for the rest of the money. This is utterly bad service and obviously the communication within the call centre is up to ****!!!