@Ahsan Thanks for letting me know, our tech team are working on this as we speak 👍
Sounds like I ran into the same issue.
I got texts on Sunday morning at 03:01 saying I had "reached 90% of your defined credit limit 250", "spent 450 or more of the cost of your plan and add ons" and your account has reached your credit limit of 250, so we've temporally stopped service on your account until the next billing date". I chatted to Three Support on Sunday morning and was told "not to worry" about the texts, and that the technical team are looking into it.
I signed in today and captured these screenshots of my current usage, along with the unbilled amount, which does not add up. It does look like a technical glitch, I'll let the team check it out.
It's also worth noting that I am also in the UK at the moment, and my roaming data cut out yesterday also.
For the benefit of the Three side; my technical team escalation no. is 3402929
Data Usage
Unbilled Events