Eh, you new to civil service ah? Why can’t an MX12 take over an MX11 post without promotion? You should actually be glad that they gave you this MX11 post. Means you will be doing work that is of a higher grade and thus stand a higher chance of getting good PG and promotion. It is NOT a must to promote you unless you have proven yourself to be worthy to take on the MX11 post. Just be grateful that you now stand a higher chance of getting promoted if you do well in your new post! If still not happy, then tell your boss that you don’t want to take up the post lor! It’s only going to be career suicide only!