Default [Q] Need help. Can only detect GSM signals.

I'm using the E975 and I've unlocked the bootloader, installed CM11 on it.

However I realised that the ROM did not detect any signals. I couldn't make calls or SMS.

I had to manually go to the network settings and find the carrier (Singtel) to register everytime I start the phone.

I then flashed savvy 4 ROM to see if the network was any better. It was, but then I was limited to GSM only. I couldn't get 3G or 4G.

Before I unlocked the bootloader, I had 3G and 4G signals.

Then I decided to KDZ back to stock ROM. I had network but only limited to GSM.

I realised my phone could only detect GSM signals from Singtel, M1 and Starhub. I couldn't see 3G or 4G.

I don't know what to do now. I need help. Must I flash any basebands or modems or anything? Thanks