@EMEL1533 

Sorry to tell you that we only provide English Service for Global users, so we tried to translate your question into English and continue to help you. Wish your understanding.

For the unstable connection issue, please provide information as below so that we can do further troubleshooting.

1. What is the light status of the TD-W9970 when it goes offline?

2. With your computer or smart phone connected to it at that time, what is the IP address and default gateway it obtained?
Note: How to get them: https://www.tp-link.com/support/faq/838/

Meanwhile, please try to access the web page and take a snapshot of the status page. 
Note: How to login to the web interface: https://www.tp-link.com/support/faq/114/

How do you make it back to work after it goes offline?

Furthermore, when did you buy it?

Here is an instruction you can follow to troubleshoot as well. https://www.tp-link.com/support/faq/2238/  

Or you can contact the local tech support to get some suggestion.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support

Have a good day.