I am making a chat GUI, but the scrollbar does not move enough. Any fixes?

I am making a chat GUI, but the scrollbar does not move enough. What it's designed to do is make the scrollingframe larger and scroll to the bottom when a new chat above line 22 (size) is present. It makes the scrollbar, but does not scroll down. Here's the code.

GUIData = {
    ChatBoxSize = UDim2.new(1, 0, 0, 20),
    ChatBoxStartPos = UDim2.new(0, 0, 1, -20),
    FontSize = "Size18",
    Color = Color3.new(1, 1, 1),
    StrokeColor = Color3.new(1, 1, 1),
    StrokeTrans = 1,
}


DesiredStyle = 2 --[[--Does 0 through 3, 4 styles--]]--

function HandleMessage(n, t, style)
    local text = nil
    if style == 0 then
        local text = n .. " : " .. t
        return text
    elseif style == 1 then
        local text = "["..n.."]: " .. t
        return text
    elseif style == 2 then
        local text = "<"..n..">: " .. t
        return text
    elseif style == 3 then
        local text = "("..n.."): " .. t
        return text
    end
end

CS = 0

function UpdateOldLabels(Parent, playerG)
    for i,v in pairs(Parent:GetChildren()) do
        if v.Name:sub(1,4):lower() == "line" then
            local LineNumber = v.Name:sub(5)
            local T = v.Name
            local LineNumberInt = tonumber(LineNumber)
            if LineNumberInt >= 22 then
                playerG.PlayerGui.ChatGUI.GUI.CanvasSize = playerG.PlayerGui.ChatGUI.GUI.CanvasSize + UDim2.new(0, 0, 0, A) --Add to the canvas size
                v.Name = "line"..tostring(tonumber(LineNumber) + 1)
                v.Position = v.Position - UDim2.new(0, 0, 0, A)
                if playerG.PlayerGui.ChatGUI.GUI.CanvasPosition.Y == CS then
                    local A = 20
                    CS = CS + A/2
                    playerG.PlayerGui.ChatGUI.GUI.CanvasPosition = playerG.PlayerGui.ChatGUI.GUI.CanvasPosition + Vector2.new(0, CS) --Auto-scroll
                elseif playerG.PlayerGui.ChatGUI.GUI.CanvasPosition.Y < CS then --Catch if the player scrolled up to view previous chats. Prevent auto-scroll if they are
                    playerG.PlayerGui.ChatGUI.GUI.CanvasPosition = playerG.PlayerGui.ChatGUI.GUI.CanvasPosition + Vector2.new(0, 0)
                end
            else
                v.Name = "line"..tostring(tonumber(LineNumber) + 1)
                v.Position = v.Position - UDim2.new(0, 0, 0, 20)
            end
        end
    end
end

game:GetService("Players").PlayerAdded:connect(function(player)
    player.Chatted:connect(function(msg)
        for _,v in ipairs(game:GetService("Players"):GetChildren()) do
            UpdateOldLabels(v:WaitForChild("PlayerGui").ChatGUI.GUI, player)
            newchatline = Instance.new("TextLabel",v:WaitForChild("PlayerGui").ChatGUI.GUI)
            newchatline.Text = HandleMessage(player.Name, msg, DesiredStyle)
            newchatline.Size = GUIData.ChatBoxSize
            newchatline.Position = GUIData.ChatBoxStartPos
            newchatline.Font = "SourceSans"
            newchatline.TextColor3 = GUIData.Color
            newchatline.TextStrokeTransparency = GUIData.StrokeTrans
            newchatline.BackgroundTransparency = 1
            newchatline.BorderSizePixel = 0
            newchatline.FontSize = GUIData.FontSize
            newchatline.TextXAlignment = "Left"
            newchatline.TextYAlignment = "Center"
            newchatline.ClipsDescendants = true
            newchatline.TextWrapped = true
            newchatline.Name = "line1"
        end
        UpdateOldLabels(game:GetService("StarterGui").ChatGUI.GUI, player)
        newchatline:Clone().Parent = game:GetService("StarterGui").ChatGUI.GUI
    end)
end)