Contradiction with 1 Kings 20:23
The servants of the king of Syria said their gods are gods of the hills, suggesting protection comes from the hills, contrary to Psalms 121:1 which implies help comes from the Lord who made heaven and earth, not the hills themselves.
1 Kings 20:23: And the servants of the king of Syria said unto him, Their gods [are] gods of the hills; therefore they were stronger than we; but let us fight against them in the plain, and surely we shall be stronger than they.
Contradiction with Jeremiah 3:23
"Truly in vain is salvation hoped for from the hills, and from the multitude of mountains," contradicts the implication in Psalms 121:1 of looking towards the hills for help.
Jeremiah 3:23: Truly in vain [is salvation hoped for] from the hills, [and from] the multitude of mountains: truly in the LORD our God [is] the salvation of Israel.
Contradiction with Deuteronomy 12:2
"Ye shall utterly destroy all the places, wherein the nations which ye shall possess served their gods, upon the high mountains, and upon the hills," contrasts with looking to the hills in Psalms 121:1, as here hills are associated with idol worship.
Deuteronomy 12:2: Ye shall utterly destroy all the places, wherein the nations which ye shall possess served their gods, upon the high mountains, and upon the hills, and under every green tree: [possess: or, inherit]