University Acceptances

I just got an acceptance from City St George but in the description it says:
The institution regards you as overseas for fees purposes and their offer has been made on this basis
I wasn’t born in the UK but I’ve lived here since I was a 2/3 months old and I’ve only ever had a british passport. What does it mean by them regarding me as overseas? Do I need to pay more? Should I email them to ask about the confusion and if I do is it possible they can take back their offer?
I also want to add that they sent me a fee questions back in december which I filled out and it asked me for stuff like my passport, citizen status etc

does it mean by them regarding me as overseas? Do I need to pay more? Should I email them to ask about the confusion
Yes, it means they expect you to pay higher 'International' fees.
You need to contact them - preferably with a copy of the fee questionnaire that you sent them in December - and ask them to reconsider your fee status.

Is it possible that they might revoke my offer afterwards?