Request for Additional Documents after Paying Right of Landing Fee

Hi,

I recently paid the Right of Landing Fee at Mississauga Processing Center for my parents which I'm sponsoring. But I got a letter from CIC saying that I need to resbumit my whole application because my mom is the principal applicant. I know that my dad is the principal applicant and my mom is just dependent on him.

This is the exact wordings that I got.
"Visa Office requested the amended document reflecting your mother as principal applicant."

And they need the Sponsorship Agreement between me and my mom; plus they want me to RESUBMIT my entire application package.

My questions are:
1. Shouldn't the CIC (Mississauga) have checked this before like at the start of processing time or even before they asked me to pay for the Right of Landing Fee? My parents have already finished their medical exams and we just need to pay for the Right of Landing Fee.

2. I had a letter before stating that CIC (Mississauga) have transferred the application process to the local visa office; so shouldn't the CIC (Mississauga) be not involved anymore?

3. Can I show them my previous application to indicate that my dad is the principal applicant and not my mom?

4. What would indicate to them that my mom is the principal applicant?

5. Any advice before I start calling them?