Accessing my computer then trying to sell me product

I really don't know how this happened.  I was trying to install IObit software.  I called the help number.  I was connected to Premiumtechiesupport.com.  I allowed them to take control of my computer, allegedly to activate the IObit product I just purchased.  I don't know if it ever was activated.  Next thing I know, the techie was showing me how corrupted my computer is.  He wanted me to buy a product from him for $399.00.  When I told him I needed to think about it and would call back tomorrow.  He said this was not possible nor was it possible for him to call me back.  He continued to high pressure me and I finally hung up.  I also changed the password on my Google account.  I sure hope he can not get into any of my accounts!  I'm embarrassed but want everyone to know what's going on!