Parenting can be very stressful at times and when a child mocks or laughs it can be very frustrating.  We think it is great that you are wanting to spend time with each of your children and you are setting boundaries for chore time and fun time with mom.  Great idea.  

When you need your 3 1/2 yo  to listen, remove distractions, such as shut off the TV or stop the video, put your hand over the toy she is playing with.  
 
Then get her to look at you by touching her face, perhaps raising her chin so she looks at your eyes, or placing a hand on each cheek so she is turned toward you.  
 
Get on her level or raise her up to your level so you are eye to eye.  Use a normal voice tone rather than a louder voice.  
 
The other strategy that parents have found helpful is to increase your praise.  If when she hears your voice, it is more likely you are praising her rather than telling her not to do something, or to do something she doesn't want to do, she will be more likely to listen.  When she looks at you when you speak, say something like, " good job looking at Mommy", or "good girl using your listening skills".

As you know spanking is not an effective skill that should be used and as you stated, it made things worse.  Give these other strategies a try and let us know how they work for you.

Boys Town National Hotline
1-800-448-3000
Hotline@boystown.org