The best way to explore the actual customer experience is through immersion research
Immersion Research is also called ethnological or observation research. They are conducted by meeting customers face-to-face and going through what they experienced, step by step, along the customer journeys. These surveys are useful to identify the pain points and difficulties they faced, and also to get detailed facts about what happened (emails, documents, photos, etc.), which help a great deal to understand the story and how to remediate.
My experience showed me that meeting 10-12 customers is sufficient to capture a great understanding of the actual customer journeys.
In these interviews, you have to look for patterns, not individual specificities. These patterns may depend on the customer types, this will lead you to create personas.