Obtaining same Forecast values for combinations

[Hemanth22]

In our major data, we have multiple combinations of customer codes and PG3 (products) that are to be forecasted using the past 3 year data. Please not that the previous year data is consistent throughout all the 36 months. 

After forecasting we are facing an issue where the forecasted values are same for the combinations, our main dataset contains 200M+ data and multiple such combinations. 

We have used both ARIMA and ETS models and customized them to achieve maximum accuracy, but when the macro is run we are getting such values.

I have attached an example of the forecast values.

Thank you in advance.

[Raj]

can you add in some same sample data.

[alexnajm]

If the data is not consistent for all months, how are you filling in those values?