Rain neglecting to change payment date before double payment

The worst service provider...been a client for the last 1 and a half years...since i started my subscription i requested that my payment date should be at the end of the month seeing that i get my salary on the last day of the month. After numerous emails and phonecalls this problem is still not solved..everymonth on the 25th my service gets disconnected and have to wait till the 30th or 32st to make a payment to have it reinstalled....so im losing a good 5 or 6 days per month...everytime i phonr them they tell me i can change it on the app to the 1st of the month but have to make a payment on the 25th aswell as on the 1st..so i have to pay twice to be able to change my payment date...so at the end of the day i must pay a double instalment for one month subscription...this after i lose about a month subscription for every 6 months