So you bought a RFM95W-868S2 from Digi-Key, they did not work at SF10-12, so what did they say when you complained ?
I do note that the RFM9x data sheet that Digi-Key link to is a masterpiece of confusion, I quote;
> The RFM97 offers bandwidth options ranging from 7.8 kHz to 500 kHz with spreading factors ranging from 6 to 12, and covering all available frequency bands. The RFM97 offers the same bandwidth and frequency band options with spreading factors from 6 to 9. The RFM98 offers bandwidths and spreading factor options, but only covers the lower UHF bands