I am teacher - timetabling issues/ feel frustrated

[charlottenina]

I have been working teaching Art in a Private sector 4-18. Initially, I was employed to teach KS3,4,5. Then it changed and I was timetabled to teach KS2. it has been for few years now and feel frustrated. talked to Head of department, Senior management- but as there are not enough classes

If there aren't enough classes in the upper school to fill your timetable then what do you expect them to do?

You need to look at your contract of employment and the teacher's terms and condition document. If you work in a private sector school from 4 to 18, then you will be expected to teach across that age range. There will be a catch-all set of phrases in the documents that say do what you are asked .
The alternative is find another post in another school that suits you better.

yes, i told K2/ KS3/4/5 in my present school. Then the school ( ? or colleagues in the department?) decided that they would need more hours and that they would rather teach those lessons...

Are you in a union? They are excellent at giving advice over the phone on this type of thing (I've rung mine a number of times!). Problem with working for a private school is often, depending on the contract you signed, they can do what they like.