Sonos can only recognize one ‘set’ of IR codes. I would expect you programmed your Sonos to recognize the IR codes that are associated with Samsung, so you would need to program your Moviestar remote to tell it that it is controlling a Samsung TV as well, so it would send the same IR codes that Sonos is expecting. 

Or, you could reprogram the Sonos to use only the Moviestar IR codes, using the normal process, and it would then stop responding to the Samsung remote. 

It’s usually better to program one of the remotes so it uses the same codes as the other, in case either remote is used. 

The Sonos Arc should be connected to the HDMI-ARC port of the TV and so be controlled by the TV (via HDMI-CEC). There's no need for ir-codes in this set up.

Is your Samsung capable of sending ir commands to the Movistar box (my Samsung is capable of controlling the STB's of the biggest TV-providers in the Netherlands this way)?

The Sonos Arc should be connected to the HDMI-ARC port of the TV and so be controlled by the TV (via HDMI-CEC). 

With my Samsung remote, I controlled all devices, including cable provider Movistar.

When installing Sonos, the samsung remote control has stopped controlling Movistar.
That's the problem.