Reneging on contract agreement

I have a contract with Rain and an agreement that stipulates that my payments will be made on the 1st of each month. Now they suddenly want payments to be made 6/7 days earlier. When you write to their support what what to raise this issue you get no response nor an acknowledgment really amateurish. Then they will switch of the internet as if I am in the wrong. This really inconveniences me and my family as I pay for a full month of service and I don’t even realise that.