Faulty phone returned within 7 days but no exchange/refund.

On 30 December 2019 I bought a lenovo cellphone. I returned it due to it not having a signal most of the time, and apps closing themselves every 2 minutes. I asked for exchange or refund as it was within 7 days as I was told. The lady told me she won't take it because according to her there is nothing wrong with the phone and the manager was on leave. I left it thinking they will call me when they have decide what to do with the phone. On 20 January I went back and was told that the phone has been fixed. Her and the other gentleman insisted that the 7 day return policy does not apply, and I should take the phone and bring it back again if it gives me problems. The phone is still giving me problems even now. Are we being ******* into buying faulty devices by claiming that there is a 7 day return policy, which then becomes a problem when you return the phone? I want a new phone or my money back.