Money is the only influence I have ever found effective. If they and their supervisor know you have the full support of whomever renews the contract, then they will be more responsive. You may have to do some digging to find their upper management and get their attention, because the person responding to you may not really care. This is assuming an enterprise scale agreement.
If you are asking about individual support from a business as you being the sole consumer, then try to find competitors. If they don't care that you are looking at competitors, then vote with your wallet and make their competitors happy.
