Unacceptable Harrassment

I made an arrangement at the beginning of this month for a debit order to be submitted on the 26th March for an unpaid premium. Cell C keeps harassing me with telephone calls, obviously before this date and the consultant keeps saying there is no arrangement in place and that's why the automatic dialler keeps calling me. Surely they have the telephone recording confirming the arrangement. Have been a customer of theirs for years, poor shoddy service