All remotes interfere with TV

I have a 32" LCD Electroview TV.

Whenever I use a remote for another device, it interferes with the TV and changes channels.

I have read other threads in this forum where the IR on the tv blocks other devices from working, however this isn't the problem I have. I have tried remotes from 3 different DVD players and they all cause the tv to change channels.

As such I can't even use a dvd player by remote with the tv. I have tried putting pieces of paper over the IR sensor on the tv, but this has made no difference. The TV remote doesn't seem to affect the other devices.

Any suggestions?

Thanks.

No I don't believe this TV had HDMI CEC, I can't see any options for it.

It doesn't make a difference, if the other devices are off, the remotes interact with the TV, so it seems they are using the same frequency. If I press a particular button on the dvd remote, it will always have the same effect of the TV such as changing it to channel 2..