The total listed in the Transaction Details Overview is the total amount initially sent with the transaction. This is adjusted when it interacts with the contract, and the difference in ETH is sent back to your wallet.
The Transaction Details tabs have more information about the contract interactions.
- In the Internal Txns, it notes the amount of ETH that was sent back to your wallet address.
- In the Logs tab, it also notes how many NaaS in the pack have matured.