A company has been established for many years and not making any growth, what is the suitable action plan to be set?

More information needs to be given. The question is not specific enough to get a specific action plan. We need to know more about why is the company not growing and whether it's loosing money or not and what are the challenges it's facing and the market condition and competitors' situation. 

pour moi in faut faire un bilan diagnostic profondn, actionner les points faibles, repenser la strategie et s'il elle a des moyens penser à des fusions ...

You need to have a good management staff:

- Marketing team:

Need to be in the market and follow up the prices for other companies and compare, also need to be creative with create a catalogue for your products/services ... etc

- Sales team:

Need to have a good sales team (Manager, supervisor and sales executives) ... etc

(... etc) = I need to know the company products/servers to be able to find a solutions for this matter.

 A proper  SWOT analysis should be done . fdurther the structure of the organization should br reviewed . is ita flat model or an hierarchy 

The problem in the company orientation and segmentation