Sorry @Shinyandnew2022 it was me misunderstanding you! I thought you had been advised to use it for 25 days as you are post menopause (now.)
Yes, if you still have fairly regular periods, then you should be using a cyclical regime of 12 days per month.
As I said in another post, there is flexibility over 12 or 14 days. It's best to keep it low and work up to 14 days if 12 doesn't control the bleeding (heavy withdrawal bleeds.)
Also, don't get bogged down in the 28 days - many women use it per calendar month - 30 days. (That's much easier than counting12 days, then another 16 and starting all over again. )
If you take it daily (100mgs) you may be fine, but the risk is your own periods will appear as 100mgs may not be enough to control the growth of the lining even when used daily.
This is why there is guidance of 12 months, or more, with no natural period or aged over 54.
What your GP won't be able to suggest are subtle variations that some consultants do, with ongoing supervision. This can be fewer days ( 10 per month) or longer cycles (anything from 6-8 weeks.)
These are options for women who have side effects.
And yes, there is the Mirena but that's always going to be a trial (of 3 months) to see how it suits you. It is a much stronger progesterone than Utrogestan which is why it usually stops all bleeding.
There is also a 3-monthly cycle form of HRT called Tridestra, for women in peri, which is 14 days of progesterone every 12 weeks. It's not Utrogestan, but it's there as another option.