2.4ghz and 5ghz wifi mac address

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Hi,

I am having an issue since I moved to my new flat with a new router set up. I am seeing hidden wifi when I connected to internet. Only recently I purchased a new PC and installed intel connectivity then I noticed in the hidden wifi disclosed my wifi mac addresses separately as hidden. In my router wifi setting, I created 2.4ghz and 5ghz with different names and passwords. First moved in my telco set as 2,4 ghz after I seeing hidden wifi I set separately. I used 5ghz and I don't want people online see my 2.4ghz, I hide it.

My questions:

1. Anyone has the hidden wifi with wifi mac addresses issue? I usually see 5ghz mac address and at times 2.4ghz mac address in hidden when I am connected to internet. From connectivity I saw them.
2. Also the telco installation man setting the router help me create a guest wifi. I have not been using but as and when saw the guest user name pop up. I try keying the password but said no such network. I log into router admin cannot find any guest wifi so can't delete or change password.
3. I have total security and vpn so wonder if I have created separately 2.4 and 5ghz but use only one is it safe to leave the other online if I don't hide it.
4. I bought up the issue of hidden wifi with my telco before I bought new Pc with intel connectivity installed. The man then helped me with the separation of 2.4 and 5 bands and checked whether the router is functioning well. With the installation of intel connectivity I can tell exactly hidden from my wifi mac addresses. Is it auto generate or someone using it?

Kindly advise what steps I need to do. Recently I receved a phishing email said they have installed trojan vrus in my PC.

Thanks!