OK, after I was waiting for a few days and no help from anyone, I tried to hire someone who I thought knows wordpress more than me to help me out and still couldn’t find the answer.
I went through everything Buzztone told me to do and read his articles as well.
This is what I found after investigating:
I went in to the back end and open the database and I found 3 strangers (administrators) who I don’t even know. So, i deleted them and change the password of everything.
I couldn’t afford to waste my time investigating anymore, so I re-install the wordpress from zero, luckily I have the old database on my computer from before the problems occurred.
I reinstall the same plugins as I had before and switched between themes and no problems anymore.
So, maybe someone hacked it and ruin my contact page so i don’t have any incoming emails from new clients.
Any opinion?