What happens if I recharge a shorter expiry plan after I have already bought a longer expiry plan?

[mibl]

I have already bought a $100 60GB 6 month expiry pack.

I will be using an excess amount of mobile data in the near future and I want to buy one of the 28 day expiry packs to supplement this.

My question is: 

If I buy a 28 day expiry pack after I have already bought a 6 month expiry pack, will the data of the 28 day expiry pack be used before the data of my original 6 month expiry pack?

[pvandenh]

You only have 1 plan at a time. They do not exist concurrently.

So if you recharge on a new plan, it replaces your old plan completely.

[mibl]

Thanks for the reply. Does the same apply for bolt-ons also?

[pvandenh]

The add-ons are done differently. So yes, you can have an add-on on top of a plan, if you just need to add some extra data.