New iPhone 5s cellular data does not come back on after using wifi

I've purchased my iPhone 5s for a week and went to the service centre 3 times ever since.

My cellular data does not come back on after connecting to the wifi, I have tried turning on and off the cellular data, airplane mode and also resetting my network settings but none of it worked. Only the classic old trick restarting my phone works which is very annoying as I keep forgetting to restart my phone and keep missing important emails.

Went to the service centre and they said it is a problem with the os 7.0.4 and asked me to update. Unfortunately even after updating my os same problem occurred, so I had to go back again and they suggested to reformat my phone and said that of it still doesn't work I just have to bare with it and wait for an update. It's been a day now and reformatting doesn't help I still have to restart my phone every single time without fail.

Question is, if it is the software's problem, why is it that my other friends who are using the iPhone 5s on iOS 7.0.5 does not have the same problem as I do?

Appreciate all feedback, thanks!