The original passage reads
“And it shall come to pass that everyone who calls on the name of the Lord shall be saved. For in Mount Zion and in Jerusalem there shall be those who escape, as the Lord has said, and among the survivors shall be those whom the Lord calls.” (Joel 2:32)
Acts 2:21 and Romans 10:13 cite “everyone who calls on the name of the Lord will be saved.” in relation to the work of Jesus. So who is the Lord here? God or Jesus.
Evidently in all three cases “the Lord” is God. But the context in Romans 10:17 shows that the Lord (God) is called on only in Christ. So by Romans 10:17 we read “faith comes from hearing, and hearing through the word of Christ”. This is what we would expect from John 14:6 “No one comes to the Father except through me.”
So in fact even in Joel 2:32, the original context, that also assumes Christ being the way that Old Testament believers will come to God, as they are raised and stand before Christ.