Cannot change Debit order date

I am so sick and tired of seeing my debit order go Of on the 20th of every month! Initially my debit order went of on the 7th. So I requested to change this to the 1st of each month. Then it got moved to the 20th, sometimes 24th of the month. I phone every month since July to try and get the debit order to the 1st of the month, but still it went of on the 24th of the month. Can someone please help me move my debit order to the 1st of the month, or at least the 30th of the month!