Distinguish the resources
A pack provides defined use for a period. Credit is an account balance that may fund eligible additional activity. A positive balance does not prove that the intended pack is active.
Check the fallback
Read how the phone behaves when an allowance is exhausted or expires. Standard usage, blocked data or an additional purchase route can differ between providers and service versions.
Keep a spare line usable
Find the actual inactivity and qualifying-use conditions. A rarely used number may need more than an unused balance. Set a reminder and test calling before relying on the phone for important contact.