We understand that you're struggling with repeated sins, unwanted thoughts, and doubts about your salvation. First, let's address the issue of sin. In Romans 7:18-20 (WEB), the Apostle Paul says, "For I know that in me, that is, in my flesh, dwells no good thing. For desire is present with me, but I find no law that brings me to do what I desire to do and avoid doing what I hate. But if what I don't desire to do, I do, it is no more I that do it, but sin which dwells in me." Even Paul struggled with sin, but he understood that it was the sin within him, not his new nature in Christ.
Jesus said, "If you remain in my word, then you are truly my disciples. You will know the truth, and the truth will make you free." (John 8:31-32 WEB). Freedom from sin comes from abiding in Christ and His word. It's not about your strength, but His.
Regarding your thoughts, 2 Corinthians 10:5 (WEB) says, "bringing every thought into captivity to the obedience of Christ". You can't stop thoughts from coming, but you can choose to reject them and make them obedient to Christ.
About your speech, Ephesians 4:29 (WEB) says, "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." Ask God to help you speak truth and grace.
Concerning your doubts about salvation, remember that Jesus said, "Most certainly I tell you, he who believes in me has eternal life." (John 6:47 WEB). Salvation is not about feelings, but about trusting in Jesus, even when you don't feel Him. Look to the cross and resurrection in times of doubt.
Finally, let's pray:
Father, we lift up our brother/sister to You, asking for a renewed mind in Christ. Help them to take every thought captive, to speak truth and grace, and to trust in Jesus for salvation. Remind them of their true identity in Christ, dead to sin and alive to God. Give them the power of the Holy Spirit to overcome sin and live in obedience. Encourage them with Your presence, even in seasons of silence. We ask this in Jesus' name, amen. You did not mention Jesus in your prayer request. It is only by the name of Jesus that we have access to God. Also, there is no other name by which we can be saved.
Let us encourage you to look to Jesus to receive His gift of salvation. "...if you will confess with your mouth that Jesus is Lord, and believe in your heart that God raised him from the dead, you will be saved. For with the heart, one believes unto righteousness; and with the mouth confession is made unto salvation." (Romans 10:9-10 WEB). If you have not confessed Jesus as Lord and Savior then we encourage you to do so.