I think you are right.. Probably the wallet address generate segwit address. So, is there any possibility for the wallet address to work together? I mean. If I send btc to the legacy address, can I find it in the segwit address?
No, the balance won't be shown.
I don't know how that wallet works. It may be possible to import a legacy address as well. But assuming you cannot import a legacy wallet, you cannot spend the fund using that wallet. However, even if you send bitcoin to the legacy address, you can import the private key into another wallet and access your coins.
Note that now you are the owner of both legacy and segwit addresses. If you send bitcoin to the legacy address, you only need to use another wallet.
By the way, why not to work with the segwit address?
You can pay lower fee using the segwit address.