Seeing default fulfillment code instead of the one hat it's used for the chatbot

I'm developing a chatbot with Dialogflow ES for a client.  
 

Situation:

• The first phase of the chatbot is already developed (months ago)
• For the first phase I was using the fulfillment feature (through Inline editor) with quite a lot of custom code
• Now, after couple of months, I started implementing some updates to the chatbot  
   

Issue: If I go and try to see and update the fullfilment code, I see the deafult code in Inline editor instead of my custom code.  
 

Questions:

• Has anyone experienced this?
• I'm thinking that one of the possible reasons could be the Dialogflow plan/version which is currently a "Free" one - although the free plan is basically just about the limits which we currently do not exceed. Could this be true?
• Or the other, more likely the right reson: I checked the settings in the Google Cloud Console and saw that the project's billing account is closed. As far as I can remember the client had to set up billing couple of months ago when we started with the chatbot development, for us to be able to use the fulfillment feature. Am I thinking correctly? Could setting up a billing again solve the issue?  
   

Additional question: does anyone know if the old custom code will be available after I somehow solve the issue above? I'm going to cry if I can't get the old code back:(  
 

Thanks, Boštjan

Answer: the issue was indeed the billing which was closed. The billing is now set again and the fulfillment works as expected.