The phone is stuck at the sony logo now.. and cant even access the recovery menu. Please. HELP..!!
I have a system backup.
Flash a boot image with recovery with fastboot.
Download this rom and install the boot image (flash boot boot.img).
Oh wait you want the stock rom back instead of installing a custom rom?
Then you have to reflash it trough firmware links are also available there.
Just flash 10.5.A.0.230 from the C6603, the only difference between the C6602 and C6603 is the support for lte(4g) which in your case(C6602) is not supported.
Flashing C6603 roms on your C6602 phone should work fine, it just ignores the additional lte(4g) modules meant for the C6603.
As bonus you'll have android 4.4.2 kitkat