Dear DWB:

You did not "sell" your soul, but you certainly invited the devil to come into your life. You need to ask God for forgiveness, which you state you have done. But, you also need to renounce the devil.

A good way to do that is what is called Renewing Baptismal Promises:

I reject sin, sand wish to live in the freedom as God's child.

Lord, all I want to is live in the freedom you offer me.
I want to reject the unloving choices I have made,
and the sinful failures to love anywhere in my life.
I reject all injustice,
all violence,
all that disrespects the dignity of all human life

I reject the glamor of evil, and refuse to be mastered by sin.

Lord, I admit that some evil has a hold on me:
it is attractive, it has such powerful rewards,
it has become a habitual way for me to be myself.
Lord, I renew my commitment this day
to turn from that evil
and from letting any disordered attachment,
any empty promises master me, 
and try to separate me from you.
By this promise, I commit myself 
to greater courage in acting justly
and refusing to let unjust systems and structures
numb my conscience or dull my heart.

I reject Satan, father of sin and prince of darkness.

Lord, as I renew my the promises
that accompany my becoming one with you
in the baptism of dying to sin and rising to life,
I know that an Enemy tries to
tempt me to sin and to many dark patterns,
I now promise to you, 
and to my sisters and brothers
who depend upon my fidelity,
that I  renew my commitment
to reject that Enemy,
and all his ways of subverting
your reign and the coming of your kingdom.

I believe in God, the Father almighty, creator of heaven and earth.

Lord, you made me and give me life every day.
I believe in you, I turn to you,
and I place my life, 
and the graces I need each day,
in your loving hands.

I believe in Jesus Christ,
his only Son, our Lord,
who was born of the Virgin Mary,
was crucified, died, and was buried,
rose from the dead,
and is now seated at the right hand of the Father.

Jesus, my Lord and Savior,
my life is in your hands.
I believe in you, I turn to you,
I commit myself to growing closer to you,
placing myself with you,
in love - compassionate, self-sacrificing love -
for others.

I believe in the Holy Spirit,
the Holy Catholic Church,
the communion of saints,
the forgiveness of sins,
the resurrection of the body,
and life everlasting.

Holy Spirit of Jesus,
Jesus promised not to leave us orphans.
I so desire to be enkindled with
the fire of your love,
that I might be renewed in courage.
I believe in and renew my commitment to
your work among us.
I want to contribute to the unity that you desire for us.
I promise to be as merciful,
for I have known your mercy.
And I pledge to live my life each day on this earth,
full of faith in the resurrection Jesus gained for me.

God the Father of our Lord Jesus Christ
has given us a new birth
by water and the Holy Spirit,
and forgiven our sins.
May God also keep us faithful
to our Lord Jesus Christ
for ever and ever. Amen.

Lord, Our God,
this year's journey to the waters of baptism
has renewed me.
I have come to know more intimately
the complexity of my weakness 
and the depths of your love for me.
By your grace, I have come to experience
the mystery of the gift of life you offer.
Please help me to remain free and faithful
that I might grow as a servant of 
Jesus' own mission.
I ask this with growing faith in
the name of Jesus, my Lord.

In our Spiritual Warfare Catalog linked below, we have many prayers, including a Hedge Prayer for Protection of Self, Prayer To Control Thoughts, Rebuking Particular Spirits, and Breaking Personal Curses and Spells.

Since you are not Catholic, if you feel uncomfortable with phrases in these prayer that are particular Catholic, you can omit them.

The Hedge prayer is to protect you generally. The Rebuking prayer is to rebuke particular demons that may attack you, such as the spirit of lust, masturbation, anger, etc. Identify the spirits by their attribute. The Breaking Curses prayer I would advise because in a sense you have cursed yourself. In this regard you should also pray, Renunciation Of Satan and Claiming the Full Victory.

We will include you in the prayers of our Prayer Warrior Team and add you to the list of the Proxy Deliverance prayers our team does each month.

God Bless,
Bro. Ignatius Mary