SMS Bundle Expiry

Hi,

Would just like to confirm the following. I have a sim card on prepaid. I add R110 airtime.

1. When will this expire? After 6 months?

2. If I buy a 20 SMS bundle for R10, when will that expire? After 30 days?

3. If I only used 10 of the first sms bundle then buy another 20 SMS bundle for R10 after 29 days of buying the first sms bundle, will both only expire 30 days after the 2nd bundle purchase date?

ie: As long as I buy a new sms bundle within 30 days they wont expire?

Thanks!