Surely this isn’t normal?

I started my new job last month and at my interview they asked if had any holidays coming up which I did, I’m going to Mexico in June and paid A HELLLA LOT for it and I’m away for 2 weeks. My work took note of these holidays at the interview.

I booked this holiday last July and been paying for it since. I booked these holidays in with my previous work then too and they got accepted.

I got access to the holiday app in my new work and tried to put my holidays through but they got declined. I said to my manager about this and she said “OH, another 3 people are off on these dates and 1 of them being someone who’s in your department and we can’t have 2 people off at once” I said, I told you at my interview I needed these but she said she’ll need to see what she can do. GUYS SURELY IF I HAVE HOLIDAYS BOOKED BEFORE I START A JOB, they’ve got to honour these??? Or else don’t offer me the job if you can’t give me these dates.

We are now 2 weeks later and she said she doesn’t think I can get these holidays and I may need to take unpaid leave for 2 weeks which will then look bad on my record. Arghhh what can I do??? Surely I can report this???