Cuba has received shipments of oil and humanitarian goods from Mexico and Russia just this year, and I don't believe that the US has done anything to stop that (although the US has heavily sanctioned Russia in general for years now). However, those good received this year appear to have been free of charge.

I'm wondering if the US is solely to blame for Cuba being completely unable to pay for the oil it needs. Obviously the US embargo on Cuba is devastating for its economy, but other states impacted by US sanctions in a similar manner seem to get by with essential good like food, oil, and medicine. Cuba is in a poor economic spot, but the US does not appear at all to be using its military to prevent them from trade with other nations.