The gas deal with China was also a GAZPROM negotiation, not Putin.You are very ill informed if you really believe that after 20 years GAZPROM negotiated the deal with China.
Russia's Putin seeks gas deal on state visit to China
There is a motto that Real Red-Blooded Freedom Loving Americans know well, that maybe on a slight chance you heard: Freedom is not free.
Ukraine does have challenges. They are working to reduce energy consumption by 30% and bring in 20% by reverse flow from Slovakia, as well as other ideas. Any short term hardship is preferable to perpetually groveling to Russia - which is run more like a cut-throat mafia than a modern civilized country.
If they can’t pay Gazprom (and note 20 yrs is longer than Putin has been in power so the Gazprom entity was the negotiator), then why should Slovakia expect to be paid?
All they gotta do is write the check. If they don’t have the money to cover the check, then time to surrender.