37 It was this Moses who said to the Israelites, ‘God will raise up for you, from among your own kinsfolk, a prophet like me.’ 38 It was he who, in the assembly in the desert, was with the angel who spoke to him on Mount Sinai and with our ancestors, and he received living utterances to hand on to us. 39 Our ancestors were unwilling to obey him; instead, they pushed him aside and in their hearts turned back to Egypt.
The clear referent here is Moses. It was Moses who prophesied the coming of one like him. It was Moses who was with the angel of God on Mt. Sinai. And it was Moses whom our ancestors were unwilling to obey, pushing him aside and turning back to Egypt in their hearts.
Of course, Stephen would also believe that his ancestors did not obey the oracles, since Moses was God's representative who conveyed God's message to the Israelites.
Stephen does not mention Jesus in this passage. Jesus of Nazareth was not alive on earth during the Exodus, so Stephen does not refer to him here - at least not directly. However, he certainly believed his fellow Jews had gone against God's will when they rejectedexcept insofar as Jesus inis thought to have been present as the current generation. (vsSecond Person of the Trinity. 52)