I accidentally bought a Large prepaid data pack, and then accidentally clicked terminate immediately instead of terminate it at the end of its term.

Hi. I was fiddling around the O2 website as I was wondering why my prepaid network internet is not working anymore. I soon realised that it is due to the lack of credit in my account, and I decided to top up my account. However, what I have not noticed is, that when I was fiddling around the website, I tried to activate the large data package and forgot to deactivate it. When I finished my topup, I received several SMS messages saying “topup successful”, “large data pack activated”, and finally “my account is low in credit” in chronological order. I wanted to unsubscribe the data pack and I misclicked the option “Cancel immediately” without noticing that it will cancel the tariff literally immediately without refunding the credit. 

Hence, can I please ask whether it would be possible to get a refund, or at least reactivate the large data plan?

Thank you.