Why does oestrogen prevent further release of FSH

The menstrual cycle - GCSE Biology?

As clear as possible please
Thanks.

oestrogen prevent further release of FSH to increase the release of LH and due to the release of LH the Ovulation phase starts

It's a negative feedback mechanism. You should be able to draw out the flow chart with the different hormones.

I don't think you're looking for the pharmacological details of how negative feedback works, are you?