Please help

My dr's prescription was for 6x repeats of a certain medicine. The medication lasts me 2 months per repeat because I was put on a low dose - by my dr. So I have been buying it every second month at Dis-chem hazeldean thus far, starting in April. When I was there yesterday for the 4th repeat, I was told that I HAVE to take the next 2 boxes before the end of this month, according to the law. Firstly, I am unemployed at the moment and cannot afford to buy 2 more repeats before the end of this month (it is an expensive product and I don't have a medical aid). Secondly, it is simply logical that I should be allowed to take the repeats every second month, as my doctor knows the product extremely well, he also knows very well the quantities of dosages per repeat, and how long the medication will last. He did not write 6 MONTHS on the prescription; he wrote REPEAT x6. Thirdly, is there really a law that specifies that one repeat of any medication has to last exactly a month? Making absolutely no provision for medications that last a patient longer than exactly 30 or 31 days? Is the law really that rigid? But this is completely ludicrous. Please. Can someone please tell me which law this is and where I will be able to look it up? And Dis-chem, please answer this complaint urgently and clarify this matter for me, as here is one of your regular customers who is without an income and will have to be without food, starting from today- if she has to take the last 2 repeats by the end of this month. Please, I am on my knees!