I have spoken against the Holy Spirit several times and because it can't be forgiven, I'm banned from Heaven forever.

The ministry of the Holy Spirit is to testify of Jesus, to point us to Jesus. When that testimony of the Holy Spirit about who Jesus is and what he came to do is fully rejected then one has truly blasphemed the Holy Spirit. Only when that rejection becomes settled and firm is there no hope for forgiveness.

How can someone know if they have blasphemed the Holy Spirit?

The fact that someone desires Jesus at all shows that they are not guilty of this sin.

Do you want Jesus? Do you want to put your faith in him? Do you seek after him at all? Then this is evidence that you have not finally and completely rejected the testimony of the Holy Spirit. The continued rejection of Jesus makes us more and more hardened against him and puts us on the path for a full and final rejection.