Do you have anything in writing with the higher salary on?
It's not very good practice! But whether it's worth challenging is really your decision, is it a lot less than agreed? Would redundancy have been a better option than the lower pay rise?
You could ask 'higher up' why you were consulted on a higher rate than you have received, or why you were consuted on a rate that they weren't aware of, as it sounds. If they have a reason which is satisfactory to you, then you could accept, and if they don't you could appeal. Are the company likely to make things difficult for you if you do challenge it?
ACAS give good advice about this sort of thing.