This work presents a model of total quality management in which the data envelopment analysis (DEA), balanced scorecard and Lean Six Sigma are combined and are implemented for the improvement of a specific organisation. The general objective of the present study is to provide a framework for improving the industry performance, finding the appropriate strategic directions, providing services at the highest quality level and, of course, achieving customer satisfaction. The required data and the implementation belong to a modern pharmaceutical industry. The customer service process was chosen as an example of the application of the methodology. Combining balanced scorecard, DEA, and quality principles, the process of 'response to customer quality complaints' is considered as a strategic customer service process. Then, the five phases of Lean Six Sigma are applied to measure and improve the level of process efficiency, in terms of customer satisfaction. The one-sample t-test method is employed to test the hypotheses, ultimately revealing that the model effectively contributes to achieving the outlined objectives. The findings highlight the benefits of implementing an integrated approach, providing valuable insights for organisations aiming to improve their overall strategy and performance while simultaneously increasing customer satisfaction.