My question here is, the way Bitcoin wallets are programed and being generated, is it also certain that old unused Bitcoin addresses (that was generated by someone but was not used or probably lost his phrase) can never be recycled by the system to be used again?
It's not that there's a database of addresses and there's a bitcoin address provider that gives an address to every user.
You can generate numerous bitcoin addresses through some mathematical calculations even without any internet connection. So, your address isn't registered anywhere and as long as the address hasn't been funded, no one can know such address has been generated.
Take note that your sim-card provider is a centralized service that has full control over everything. In bitcoin, there is no third party at all. No one has control over addresses and transactions.