I am being bul**** by the organisation for the second time

I am being bul**** by the organisation for the second time. They have been double debiting me since end of May. They claim I am behind with one payment, which they can’t prove. I agreed to pay the installment they claim is behind but they are not being reasonable with the time of payment. They have my services turned off for the whole month at this point and they are refusing to meet me halfway