– wallet was compromised and btc stelon

I lost some money in a ico scam and googled and found a reclainfund ltd to recover fund. They ask me to set up a account and then share account wallet id and password so they can transfer stolen fund. I did that. then I transferred 0.51 btc to my account and then changed my password. now it seems to be hacked and my btc is gone and all transaction history is gone. The weird thing is the blockchain’s account left panel is totally empty now once I login and I can’t see any transactions. how could that happen ? I wonder if someone inside is associated with hacker or scammer. that is really some high level scam I have ever see.

my question is in my account, where is the private key that they can steal and copy and it can bypass my changed password ?