Changed from Vodafone to Telsta?

So I changed today from a vodafone sim to a telstra one. I have the sim in and everything and I've called the 1258887 activation number and it said it should be activated so I can receive messages and all in 12 to 24 hours. I told them I wanted to be on the $30 pre-paid cap option. So if I go to buy credit (which I do at a shop when I'm getting food or other stuff because it's just easy to add it on top of whatever else I'm buying), if I just ask for $30 Telstra credit will it automatically put me on the pre-paid cap thing so I'll get the $170 bonus, or will it just be a normal $30 credit?? Sorry if this doesn't make sense I'm just kind of confused and I'm going to get the credit tomorrow.. ??