There are two references in the Bible which refer to the “unforgivable sin”.
(1) Matt 12:31-32
"Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. Anyone who speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, either in this age or in the age to come.”
So, there is an unforgivable sin, but notice that Jesus said God would forgive all the other sins, if only you ask. The agent that God uses to pull people to Jesus for salvation is the Holy Spirit, so many people believe that if you commit this unforgivable sin you wouldn’t want to repent anyway, since it is the Holy Spirit that draws you. Your continued desire for salvation is a sure sign that you have not committed this sin. If you had committed that sin you would have no desire for salvation.
Also, some say that the unforgivable sin is when a person is at his death bed and his last words still denounce God and his unbelief in Jesus, and renounces that Jesus can forgive sins and save him from Hell. This person would turn his back on Jesus and not only refuse to seek redemption but would also condemn it…
Other unforgivable sins that can be committed are referenced in The Book of Revelation:
(2) Rev 14:9-11:
“Then a third angel followed them, saying with a loud voice, “If anyone worships the beast and his image, and receives his mark on his forehead or on his hand, he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb. And the smoke of their torment ascends forever and ever; and they have no rest day or night, who worship the beast and his image, and whoever receives the mark of his name.” NKJV
Therefore, in my opinion, there are unforgivable sins, but they all add up to those who turn their backs on God, by means of the Holy Spirit, and even denounces His existence up to and at the time of their deaths. Also, (ref: Matthew 12:31-32), in one of the biblical footnotes on “Unforgivable Sin”, the definition states: “The sin of attributing good works to Satan instead of to the Holy Spirit.