Hi @dhinakar2707,
Chances are that you have a reference to mongodbatlas in a module which does not declare where that provider is sourced from with required_providers, so terraform is guessing that it must be in the default hashicorp namespace.
You can see what providers terraform finds using the providers command. If it is coming from a module, the solution would be to add required_providers to a file within that module. If that doesn’t work for you, we would need to see a complete configuration example here to debug.