Unblocking my apple account

Hi all,

I had my Ipad air 2 stolen in 2016 in the USA. Unfortunately not covered by insurance due to it being in a rucksack on the back seat :( .....more to the point in panic mode I set up authentication and locked the account.

I received an email today telling me my icloud is almost full on that locked account.

Does this mean someone is still using that Ipad and icloud?

My problem being, I have never been able to unlock the account due to needing a code sent to a USA number I no longer have to gain access or sent the original device which was stolen. I have a recovery key which was set up at the same time and i know the password but when trying to log in I need the code and when trying to change this detail I get a message that i have tried to log in to many times.

Does anyone know a way out of this loop to recover my account? When I last contacted apple in 2016 they couldn't give me any assistance.