Landline disconnect at night but dsl working

Landline disconnect at night but dsl working in morning ptcl start working again plz tell me whats the problem?

It could b bcoz of some sort of a maintenance work going on. Ptcl is trying to upgrade its coper infrastructure to fiber. You might wanna visit your exchange in person to get more answers.

I had the similar issue and I was told that the lines are being upgraded.
I could b wrong but still would want to share my experience.