Bad service

My data dissappers and vodacom blames my iphone settings. The weird thing is that it does dissapear all the time, it is certain months and always beggining of the month. So if they are blaming my phone, they are telling me I change my settings during those periods when the data disappears and fix the settings the other times? my argument is I have had the iphone for my than 2 years I know what to do to save my data. Who wants to keep buying data for it to disappear? So why would I be fiddling with the settings that works. Last year (2015) this happened in May and August, my data disappered so all the other months my phone had the correct settings and those two months I decided to change settings please? On the 2nd of Jan 2016 my 500meg dissapered again and I was told they will investigate as usual but till today it is not resolved. This is not funny, I hate calling the call centre to be reporting this as they make you seem stupid. Can vodacom please sort out this.