The idata bolt on is usually an easy thing for O2 to apply, so I have no idea whether the system is glitching or not. In fact I've no idea why it wasn't on at the time of purchase.
You can only persevere with customer services... until you find someone who knows what they are doing. Also take a look at this guide https://community.o2.co.uk/t5/Apple/Connecting-iPhone-to-Data-Services/m-p/544210#U544210 and see if it helps?
They won't be on until Monday though.
Best of luck and welcome to the forum
Veritas Numquam Perit
The iData bolt on should not effect calls and texts so there is another problem here.
Your SIM may be faulty, so I would try a SIM swap too.
Any O2 shop will do this for you for free.