Do I get my proficiency bonus with Shillelagh?

Question

I am considering picking up the Shillelagh cantrip as part of my book of shadows pact boon as a level 3 Warlock.

The spell description states that I get to use my spell casting modifier (Cha + 3) instead of Strength for attacks. Does that mean I still get to add my proficiency bonus (+2) to the attack since I am proficient with my staff?

The wording from the PHB is below

The wood of a club or quarterstaff you are holding is imbued with nature's power. For the duration, you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks using that weapon, and the weapon's damage die becomes a d8. The weapon also becomes magical, if it isn't already. The spell ends if you cast it again or if you let go of the weapon.

Answer 1

If you are proficient with a weapon, you add your proficiency bonus to attack rolls with that weapon. The spell does not change that. Warlocks are proficient with simple weapons, which includes the quarterstaff, so yes.

Answer 2

You are close don't have it quite right. What the spells does is substitute the Strength bonus for whatever bonus from the attribute you use to cast spells. So if you were a warlock with a Strength of 12(+1) and a Charisma of 16 (+3) and cast the spells then all your to hit modifiers would calculated with the +3 bonus from charisma instead of the +1 bonus from Strength. Your proficiency modifier and any other modifier would be added in normally. The same with your damage modifiers.

This is with the limitation that it only applies to melee attacks.

The key phase is

you can use your spellcasting ability instead of Strength for the attack and damage rolls of melee attacks