Premium debited on wrong date

I took out a funeral plan with 1Life last month in March on the sales call I mentioned that they should debit the premium on the 20th of every month starting from the 20th of April 2016. I even mentioned to the consultant by the name of Siphamandla that I had a bad experience with other service providers where they would debit my account whenever they wish to. I emphasized on the 20th and he said he had put that into record however my account was debited on the 1st of April I called 1Life on the 4th April and requested to speak to a manager who said he will sort out my issue before end of business but still haven't got any response. I received an sms today 06/04/2016 saying that they will debit again in the middle of next month. my account is already on negative balance due to them debiting on the wrong date so they going to debit again and still leave it on a negative balance. I want them to pay for my back charges or cancel the policy, I took out this policy as its suits my needs and is affordable however it is inconveniencing me because they are not reliable.