I think the original responder's concern, which I share, is that your question is really an opinion, rather than a genuine question, and that they (or I) would spend time writing a long, detailed response to what is a very complicated topic, only to be wasting our time because it would fall on the ears of someone who is not interested in listening (or reading).

I'll go for it though, and address the original question, which was 'If everyone is so united in opposition why are they still buying the oil and gas (paying in Rubles)?', although you've rephrased it as 'please explain to me how all the European countries that are so united in solidatary with Ukraine can square the round hole of also paying Russia vast sums of money for energy?', and somewhat differently asked 'I don't know how paying Russia helps Ukraine, or are they not paying for energy?'

First off, I don't think anyone would argue that this in any way helps Ukraine. Of course, paying money to Russia is not going to help Ukraine. However, Europe has been dependent on Russian oil and gas for a long time, and it is not simple to just cut that off. 40% of gas supplied to the EU comes from Russia, and almost 30% of the EU's oil.

Second, I don't think anyone anticipated that this war would last longer than a month or two. I think the expectation from the EU's side was an overwhelming show of force from Russia, regime change in Ukraine, and a quick end to hostilities. Although the EU started discussing longer term moves away from Russian gas and oil at that point, I don't think there was a sense that this could have any short term impact in terms of supporting Ukraine (or cutting off indirect support for Russia). The EU, known for being slow to react and full of bureaucracy, was able to publish a plan on 8th March, less than two weeks after the invasion. The plan is very aggressive, and targets reducing imports from Russia by two-thirds within one year. This is a major economic blow to Russia, and likely was intended to scare Russia into changing their approach in Ukraine, unsuccessfully.

Third, just stopping paying for this fuel would likely be in breach of commercial agreements. Russia and Ukraine have been at war since 2014, and the EU has not stopped paying for gas. There are legal implications to not upholding your side of a contract, although I doubt that this is a serious consideration - likely this could be thrashed out quickly.

Fourth, if we stop paying, Russia would then cease supplying oil and gas to the EU. There are a number of reasons this would be problematic. First of all, the distribution systems we currently have need to be pressurised (this is not technically quite accurate, but it's a close enough analogy I don't think it's important to get into the details). If Russia stopped supplying gas and oil to the EU, there is an overhead for the EU to keep these pipelines pressurised to avoid the whole system collapsing. So additionally to losing 20-30% of Europe's fuel supply, Europe would additionally need to divert supplies to the network rather than it being available for use by users. I wasn't able to find details on the amount of technical gas consumed by the EU and what the gap would be, but during the previous fuel crisis, the gap for gas alone was 21 million cubic metres per day, which represents 2% of the EU's total daily consumption.

Fifth, the EU is struggling with economic challenges same as the rest of the world. We have high inflation, Cost of Living is going up faster than salaries. Reducing energy supply would necessitate massive price increases on fuel bills, which is currently being seen in the UK and very poorly received. As this war seems to be settling in to become a long, drawn out conflict.

Finally (at least for this comment), from a military strategy point of view, cutting off this income now would give Russia the opportunity to develop other income streams while operating on their reserves. Waiting until Russia is deep in an economic crisis, and has burned through their war chest before cutting off their cashflow is likely to lead to more acute hardship and be a stronger bargaining chip. I'm sure Russia are currently considering this as well, but there will be a 'sweet spot', before Russia are able to develop other income streams.