Hi Mauro,
I have created a sample c# extension project to Call a stored procedure that is returning multiple datasets. Please find the attached extension for the same.
1. You need to create a database connection string in service studio.(Below is the screen for the same)
2. You need to change connection string name, stored procedure name and input/output parameter in this extension project.
You can refer below course for Extending Logic with C# Code -
https://www.outsystems.com/training/courses/117/using-c-code/

Thanks
Vinod