Ad removal

In order to prevent me being beleaguered by irritating ads in my inbox I pay, via a monthly standing order, the required 00.79p.

However, the first two weeks of each month seems to ignore this standing order by displaying ads in all their irritating glory!

It has to be said that they do go away after 2 weeks , which means that my .79p is only Valid for 2 weeks in each month.

Is this correct and, if so , How do I get cover for an entire month?