Hi I work for a company that gave me a contract in September stating 37.5 hours mon to fri and now we have to stay behind xtra 30 minutes on some days and work one Saturday in four with no xtra pay. One colleague has been fired for showing her feelings

It depends on EXACTLY how the contract is worded.

It says go to summary book they gave us, it says 37.5 hours per week 11 am till 7pm and even that's wrong as we work 10-7.