Incorrect payment

Unimet ,I paid the incorrect amount to unimet and called for in assistance with refund the amount was is all I am left with and i have kids i wanted to make payment of 200 for water and not 2000 now Unimet refuses to make a refund to my account for the money that i have paid, How will i live the whole month with 3kids , I have nothing in my account now , please help