What can i do if im unable to verify my id online an unable to reach anyone on the phone. I already mailed the taxes in almost 3 weeks ago. Idk what else to do?

I recieved a 5071c letter an have not been able to verify my id. Ive done all that i know to do with callin an tryin online without success. So i mailed them in 3 weeks ago. An still nothing, idk what else i can do?