Welcome @Amal
You haven’t told us about your guarantor’s situation, how much they earn, how many dependents they have, is there any family relationship between you?
At first glance, I would say that the reason for the visa refusal should be sought on the financial side: how do you plan to pay your tuition fees, which are still significant? Did you make a partial blocked account, for how much?
What’s the name of your school? A letter of support from the school, in my opinion, doesn’t help at all. You need to properly prepare your application, you should get your visa. And your accommodation, how much does it cost?
Best regards