Your application of these verses is in direct contradiction to what is taught in Hebrews 6.
This passage says that the "natural branches" who were broken off can be grafted in again (i.e. saved again) by God if they do not continue in their unbelief. But Hebrews 6 says that if one falls away, it is impossible for them to come to salvation again. Therefore, it is impossible that the "natural branches" spoken of in this passage refers to people who were once saved, then lost their salvation. The only conclusion that does not contradict Hebrews 6 is that these "natural branches" were never saved in the first place.