Just as a return to the forum, here is my progress and result how the C permit granted:
B permit in 2011 from the beginning, after 10 years B the MigrationAmt ask me to renew the B permit. In August I visited them and checked if I am eligible to apply for that. The answer was positive and they said that I only need to mention in the B permit extension.
on 23th.August I submitted the application and it came back rather quick, they asked me to provide few documents:
1, no debt record in last 3 years
2, no social security applied in last 3 years.
3, language A2 cerfiicate
4, payslip and contract
5, statement that we dont have other child except those who applied the C permit this time.
We gave all required documents back on 1st.Sept.
the C permit arrived today. It takes roughly 7 weeks.
It might because that they wait till the B permit expiry.
Good luck to all who applied and are going to apply.