Sanlam Sky is ripping me off!

I have a policy with Sanlam Sky and I've had this policy for almost 5 years. I have been paying for my policy every last day of the month since I get paid on the last day of the month. Of recent i have been getting smses saying that my payment is overdue and an additional cost has been added whereas it is not even the end of the month! Is Sanlam trying to make money out of this, by ripping customers off in the name of arreas?? I feel that I am being ****med here! The last time they did this to me, they said that they will fix the issue and then i let it go. This time I want to take things further!