If you are using a none original remote then not all remote codes will work all the functions. Some codes are designed for different models. So you might have to try several codes before all functions will work. Even then some might still be missing.
If you are using a new genuine remote and it's still playing up. Then either two possibilities can occur. The set has been switched to work a different remote. Or there's a fault in the set that has either effected the remote functions or has caused the functions to cease to operate, even though the remote is sending out the correct signal and the set has received it.