Client contradicting our agreement

My freelance contract states “paid at a rate of £x per hour & the work is expected to take up to x hours per week on average with additional hours as mutually agreed” it goes on to say I can “choose when hours are worked”. My understanding was that the weekly hours are a guideline highlighted by use of words “expected” & “on average”.

Unfortunately, newly hired Director I report to views the expected hours per week as fixed, in fact they’ve proposed going forward I work set hours on set days, & ask their permission to work outside allowance. Any ideas on how I respond/ move forward? The set days completely contradicts my agreement, but am I right in thinking that the hours per week are not set in stone?

Many thanks in advance!