Circle that exists only when a gui tool is selected?

So what this excerpt from my script does is that whenever an attack (gui button) is selected, it selects it and checks for "AOE". If there is a value for "AOE", then it makes the aoecircle appear under the player with a circumference of the AOE. My problem is with removing the circle; how do I make it both remove the circle from Workspace, set the variable nil, but at the same time stop the "RenderStepped" coroutine from running? Currently, it sets newaoe to nil and then RenderStepped returns hundreds of error messages, essentially crashing the game. Any help would be appreciated!

local aoecircle = Instance.new("Part")
aoecircle.Anchored = true
aoecircle.Transparency = 0.5
aoecircle.CanCollide = false
aoecircle.Material = "Neon"
aoecircle.BrickColor = BrickColor.Red()
local aoemesh = Instance.new("CylinderMesh",aoecircle)
local newaoe = nil

function changeStats(atk,bar,info)
	a1:FindFirstChild("AttackName").TextColor3 = Color3.new(0,0,0)
	a2:FindFirstChild("AttackName").TextColor3 = Color3.new(0,0,0)
	a3:FindFirstChild("AttackName").TextColor3 = Color3.new(0,0,0)
	a4:FindFirstChild("AttackName").TextColor3 = Color3.new(0,0,0)
	if selectedAttack ~= atk then
		selectedAttack = atk
		selectedBar = bar
		selectedInfo = info
		selectedAttack:FindFirstChild("AttackName").TextColor3 = Color3.new(1,1,1)
		cas:BindAction("useMove", attack, false, Enum.UserInputType.MouseButton1)
		if selectedInfo["AOE"] then
			newaoe = aoecircle:clone()
			newaoe.Size = Vector3.new(selectedInfo["AOE"],1,selectedInfo["AOE"])
			newaoe.Parent = game.Workspace
			coroutine.resume(coroutine.create(function()
				game:GetService("RunService").RenderStepped:connect(function()
					newaoe.CFrame = game.Players.LocalPlayer.Character.Torso.CFrame - Vector3.new(0,2,0)
				end)
			end))
		end
	else
		selectedAttack = nil
		selectedBar = nil
		selectedInfo = nil
		cas:UnbindAction("useMove")
		newaoe = nil
	end
end