Hi latoya and Welcome to the Forum.
What's has happened is that you've been charged £1 for connecting to the O2 internet without an available data allowance. This is called Web Daily and this gives someone 50mb of data use for that day ~ more here
http://service.o2.co.uk/IQ/SRVS/CGI-BIN/WEBCGI.EXE?New,Kb=Companion,question=ref(User):str(Mobile),C...You have a couple of options.
Turn Mobile Data off in your phones settings ,and top up with the minimum £10 ,and your allowances will refresh on your tariff and then you can turn Mobile Data back on to continue to use any data allowance.
You could try contacting O2 Customer Services via Live Chat or phone call and explain what's happened ,and as a Goodwill Gesture they may replace the £1 especially if you didn't use the 50mb of data given for the £1, and then your allowances will refresh.
If you choose not to have a data allowance in your Payg Tariff then perhaps leave Mobile Data turned off in your phones settings to stop this happening again.
Points of contact to O2
http://www.o2.co.uk/contactusGood luck.