It shall be unlawful for any mortgagee, vendor, holder, or lender in connection with any insurance required as additional security for a loan on real estate to make any separate charge to either an insurance company, insurance agency, borrower, mortgagor or purchaser other than the insurance premium on insurance written in connection with such transaction according to law: Provided, That the term “separate charge” as used in this act shall not include the interest which may be charged on premium loans or premium advancements in accordance with the security instrument.