Why is my IMEI blocked?

My name is Vínicius and I'm from Brazil, I've never left my country. I've had my current cell phone (UMIDIGI A9 PRO) for at least 3 years and it's never had any problems but for a while I stopped receiving SMS out of nowhere and tried to fix it on my own and reset my cell phone. To my surprise it got even worse because now I don't have a mobile network and I can't access most of my accounts that have 2FA because I don't receive SMS remember?

And there I went looking for a reason for that and I found out that AT&T blocked my IMEI due to loss or theft, according to the telephony agency in my country (Agência Nacional de Telecomunicações, ANATEL).

I went to ANATEL to ask for a direction and they said that only those who placed the block can remove it. I never subscribed to any of your plans of any kind, my only cell phone operators were Brazilian.

And here I am, I lost my cell phone number here in Brazil due to inactivity, and with it most of the things  and I can't use any other number because I'm blocked for no reason.

Can you help me?