Unhappy customer

I usually pay my Rain account on the 25th of the month. Last payment (debit order) was collected on the 25th of February 2026. On the 19th of March 2026 I changed my Debit Order date as this month I will only be paid on the last day of the month. Rain says my account is "OVERDUE" and full payment should be made. My question to them was "When I changed the Debit Order date, the account was not in arrears, why is it in arrears? Right now Rain expects me to pay (which I paid yesterday the 25th March) and again on the 1st April 2026. They are not willing to understand and help sort out this matter, they just want to collect double on my side. Please help resolve this unfortunate situation.