*****ing my money

Im very confused. You know i read my contract over and over again and in my contract it doesnt state that my installment must change monthly unless i have consented. My account was never in arrears and i signed an agreement for a certain installment but every month a little more is added on my installment with no communication. One of the people working there spoke about interest rates so the interest changes every month and also this is a loan not a BOND i want a break down of why my installments keeps changing and a statement on what ive been paying so far. Please also dont get someone to call me because i always get a whole lot of lies. I want a full explanation on email.