Hi @Daniel_Santiago_Rocha_Morales and welcome to the community forum. 
To help you triage further, could you help me understand if you are seeing the similar issue while working on the shell?
If yes, could you confirm if you are using the correct customer_id in the upsert query.
If the issue only persists on the application end, could you help us with some stack trace and some logging information by adding DEBUG level logs in the above condition?
Best Regards
Aasawari