Generally only the people who supplied the bottles will refill them. The suppliers have to factor cylinder testing / replacement into their costs.
Most bottles these days are owned and leased by people like BOC or Air Products, and they will only refill their own bottles. If your bottles originated with one of these then you might be able to find someone else with an account who will swap the bottles for you.
Otherwise maybe an independant will do you a deal. Else Energas are in your area and are slightly cheaper than BOC/Air Products.