you dont need b.com to do CA.
If you're in lahore, just go to ICAP office on thokar niaz baig. Walk right in and ask them about CA and how to do it.
I don't know what ICS is, but all you need is fsc or equivalent with 60% grade.
CA is bunch of papers. Once you clear them, then it's 3 and half years of article ship. This is where you go to an accounting firm and do training, after this 3 and a half year training you appear for final papers. If you pass them, then you are an ICAP member and can practise accounting publicly.
The papers before you can start this training would require a minimum of 1.5 yrs if you can pass all of them in first attempt. There are 3 attempts per paper. No time limits.
With a b.com , I think they exempt you from these papers and you start with training straight away (that's how it used to be, now sure if it's still like that).