Instead of manually parsing this; why don't you look at what you have, and then use the properties to get what you need.
In this case, you have JSON. This is an object that has been serialized into a string format.
What I would do is:
1. Create a class with a design parallel to your JSON.
the JSON into instances of that class (objects)
3. Read the desired properties from those instances.
Deserialize an Object
How to serialize and deserialize JSON using C# - .NET | Microsoft Docs