Better LTD extra puchase mechanism

Could you provide an auxiliar credits package?

When user reach out 7000 messages credits, automatically connect to use that auxiliar credits.

Let's say I puchase currently package of 1000 messges credits, those credits will be used when the 7000 are used in the 25 days of month calendar, in that 5 days the 1000 are used 50%, it still available 500 messages credits, but after the last 5 days my 7000 montly messagges credits are available again, so the automation is the bot will switch to consume the montly credits, saving the 500 for next time when the 7000 are reach out again.

If the 500 message credits are finally consumed, then the system will ask me to recharge again the auxiliar package.