Well We all know According to spoilers Ruhi called Raman from School;
Here are some reasons I thought about regarding Divyanka's Absence & Paternity Issue.
#1- We all know Schools have medical tests She may have called because Of this and the school staff wanted her mother or father to be
Around, Ruhi would under go a blood test & Raman will sill the reports and It will be clear that He is Ruhi's father.
#2 - Ruhi may have started feeling ill thus She asked her teacher to let her talk to her Papa, Raman takes her to a children hospital and then The doctor says we have to check Ruhi and again Blood test OR Raman may think to clear his doubts and ask the doctor to do a DNA Test.
#3 - Ruhi may have called Raman so that her mother's name in the school could be changed as we know School people keep a record of the parents of a child thus Raman would go and update it to Ishita's name.
#4 - Ishita couldn't receive Ruhi because She was busy with her conference thus Ruhi called Raman to pick her up
That's it! All I can think of!
Feel free to share your views too!