I've sent my BTC to a new address, then imported the private key to BCH wallet from my previous BTC address. In the BCH wallet, I see the same transaction done, and thus there 0 BCH balance. How do I get my BCH in this case? The transactions was made in 5 of august.
What BCH wallet are you using? I've seen this problem in Electron Cash when it is connected to a BTC server (basically you are still seeing the BTC tx even when using a BCH wallet). If this is your case then make sure you disable automatic server selection and connect to a BCH server.
You can use any Bitcoin Cash explorer (e.g. Blockdozer) to confirm your address has non-zero BCH balance.