I had this experience with Jones Oil around this time last year. I have been a customer for a number of years with a budget account. I phoned and they agreed to the internet price immediately and credited my account with the difference. They may have been more amenable because I've had an account for years and were afraid I'd close it.
Insist on the lower price and if you make enough of a nuisance they may give in. With other suppliers I've found looking to speak to the CEO gets results that frontline staff are unable to give. Jones Oil CEO is Pat Nevin.