What is worse than paying through the nose for heating oil? Paying a bargain basement price, then realising you've been scammed.
Run your eye over this archived web page (you may have to scroll down). Apart from the slightly unconventional spelling - nextday, sameday and a missing questionmark - is there anything about it that looks not quite right?
For one, most companies, even small ones, are suffixed Ltd for limited liability; to use those letters without limited liability is a criminal offence. Notice anything else? How about something that you might expect to be there - a telephone number? The reason the phone number does not exist is because neither does the company. The individual or people who set up this website are quite likely domiciled outside the UK. The domain has now been shut down.
You can read about some of their victims here.
This is another form of fuel bilking, only this time it is the goods that are not delivered rather than the payment.
It goes without saying that you should never deal with an on-line company unless it is a household name or you have some sort of guarantee that it actually exists.
You can check out any UK company via the Companies House website, and if you want some general advice about avoiding scams - on-line and in the real world - download this free guide. It's aimed at the elderly, but anyone of any age can be taken for a mug. Just make sure you aren't!