I'm not sure if a mortgage broker will give you much help in refinancing.
A mortgage specialist with your current lender probably can give you better suggestions on how to make things work for you.
If you still have a large amount and/or a fairly long time left inyour existing mortgage contract, refinancing the current mortgage per se to a lower rate could result in siginicant prepayment penalty. You have to know how big the number is before deciding your course of actions.
If the penalty would be steep but you really want to do something to bring down your interest rate, what you can consider is to keep the current mortgage intact, refinance only the "top-up" amount up to 80% of the property value, and essentially keep a 2-component mortgage with different interest rates and terms. You then use the fund from the 2nd (refinanced) component to pay off your higher interest debt (if any). For example, exhaust and maximize all prepayment options allowed for your first mortgage, if you have not been able to do so before. This way you will take on more debt, but offset the interest rate on your existing debt.
This may or may not work for a specific case, depending on one's debt load structure. Do the math and see if there is a magic balance point for you.