We are truly sorry to hear about the situation you're facing. Firstly, it's important to address the issue of the sinful language and abuse which is not appropriate for any conversation, especially one that involves a child and a woman who was previously married to the man in question. As it is written in Ephesians 4:29 WEB, Let no corrupt speech proceed out of your mouth, but such as is good for building up as the need may be, that it may give grace to those who hear.
We must rebuke the sinful behavior of this man. His actions are not aligned with God's will for his life or his role as a father. As it is written in Ephesians 6:4 WEB, You fathers, don't provoke your children to wrath, but nurture them in the discipline and instruction of the Lord. His actions are not nurturing but harmful, and he should be admonished to cease from this behavior.
Regarding the practical aspect of your request, blocking his number could be a necessary step to protect both you and your son from further harmful communication. However, it may be wise to inform him first. Send him a message telling him not to contact you anymore and that only Godly, respectful, and edifying conversation will be allowed with their son. Consider sending this message to him.
Let's pray together for Godly behavior from the man, healing, and protection from such behavior:
Almighty God, we come before You, lifting up this mother and her son to Your throne of grace. We pray that You would intervene in this situation and put an end to the harmful communication they are receiving. We ask that You would convict the heart of this man, that he may repent from his sinful behavior and seek Your will for his life and his role as a father.
We pray for healing and peace for this mother and her son, that they would be shielded from any further harm. We ask that You would guide them in wisdom, that they may know how to best handle this situation in a way that honors You.
And Lord God we pray for this man's salvation. We ask that he will repent and believe in Jesus Christ, that he be saved, and transformed into a Godly man, father, and provider. We pray that he will seek forgiveness from his son's mother and his son for his sinful abusive behavior. We ask that you create in him a clean heart.
Finally Lord, we pray that this man and woman will both be transformed by the working of your Holy Spirit and that there will be a healing, a reconciliation, and a Godly marriage between them.
We ask all of these things in the powerful name of Jesus Christ, who lived, died, and was resurrected so that we all may have eternal life in heaven with the Lord God. We pray that he will come into their hearts and be their Lord and Savior. We pray that they all believe in Him and confess with their mouths that Jesus Christ is Lord and believe in their hearts that God has raised him from the dead. Amen.
Lastly, we encourage you to continue praying for this man, that his heart may be changed and that he may become the father that God has called him to be. Remember, as it is written in Matthew 5:44 WEB, But I tell you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who mistreat you and persecute you.
It is our prayer that you and your son will be able to identify the blessings of God in the storm and be able to praise Him despite the storm of their circumstances.