If the gas supplier hasn't done any testing after being informed of your concern about a leak you seriously need to find a different supplier. Call a few different ones, explain the situation and see what they'll do. If you don't own the tank and are only renting or leasing it from the supplier most other companies won't touch it.
If you own the tank, definitely find a new supplier.
If you are leasing it then still call and see if other companies will take a look.
I've been told by more than one LP supplier that the company they purchase their gas from have very specific rules and regulations to what they must do. Responding appropriately to any reported gas leaks is very near the top of the list.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.