What you don’t know is a lot of the Russian gas goes missing. The money from the sales ends up in Putin’s buddy’s pockets and in the pockets of their comrades in Ukraine. “Officially” neither the Ukrainian or Russian government was involved.
Gazprom essentially has a license to steal. The unpaid bills only get noticed occasionally by the criminal syndicate when it suits their purpose such as now. Other times it’s business as usual with the criminals getting their cut. Just like the Mullahs in Iran who are beyond filthy rich you have the same deal in Russia.
If there is no corroborative evidence, then how do we know that the missing gas ended up in Putin's pockets or in others’ pockets.
If we do have evidence, then the gas is/would no longer be missing - we would know here it went to.