O2 supposedly unlimited internet

So I bought a new phone and it came with a sim card. It supposedly has unlimited internet but if you use more than 10Gb a day you have to ask for 2 more. At least that's what I understood, the problem is I don't know how to ask for more and I can't find how to do it anywhere. All I found out was that they were supposed to send me an sms or something but nothings happening. Does anybody know what to do?