Random ARC Picture Size Change. While watching the tv, the size of the picture changes as if the

Question

While watching the tv, the size of the picture changes as if the ARC button is being selected. We have had the tv for a month and the problem occurred a week ago after my daughter had 'played' with the remote control - I think she held down the ARC button!I have tried the usual things ... turning off the power to the tv, selecting another tv size through the ARC button, and resetting the factory settings through the Menu options, but this only works while watching at that time. If I then watch something on Sky that has been pre-recorded the problem comes back.Any suggestions?Thanks.the picture of the becomes smaller than that of its original size