Oppo A18 IMEI Blocked Without Warning - Device No Longer Usable

I am using an Oppo A18 device and on the night of 20 June 2026, around 12:00 a.m., I found that my device has been banned. Since this ban started, I am unable to use my device properly and I want to clearly state that I did not receive any prior information or explanation about this situation. I have not yet contacted customer service, the seller, or the network operator; the first place I am explaining this situation is here. I request that the ban on the IMEI and device of my Oppo A18 be urgently removed and that my phone be made fully usable again. I also request a clear written explanation of why this ban was applied, and if it was a mistake, I want it to be corrected as soon as possible. I expect this issue to be resolved quickly so that I can continue using my Oppo A18 device without any restrictions.