Export multiple variables to csv

I am a bit lost in adding my results to a csv.

I tried several way, but the objects are not written to csv.

##########################################################
# Var
##########################################################
$wdb = Read-Host "Enter Mailbox Database"
##########################################################
add-pssnapin microsoft.exchange.management.powershell.e2010
Import-Module ActiveDirectory
$ADSettings = Get-adserversettings
If ($AdSettings.ViewEntireForest -ne $true) {
	Set-AdServerSettings -ViewEntireForest $true
	}
##########################################################
function Get-ADUserLastLogon([string]$userName)
{
  $dcs = Get-ADDomainController -Filter {Name -like "*"}
  $time = 0
  foreach($dc in $dcs)
  { 
    $hostname = $dc.HostName
    $user = Get-ADUser $userName | Get-ADObject -Properties lastLogon 
    if($user.LastLogon -gt $time) 
    {
      $time = $user.LastLogon
    }
  }
  $dt = [DateTime]::FromFileTime($time)
  $AdvStats = Get-mailbox $U.SamAccountName | Get-MailboxStatistics
  Write-Host "$($username) last logged on at: $($dt), the Mailbox was last accessed on $($AdvStats.LastLogOffTime) by $($AdvStats.LastLoggedOnUserAccount).
  The mailboxsize is $($Advstats.TotalItemSize) and contains $($AdvStats.ItemCount)."
	  $Item = { 
		  @{
			  $Item.UserName = $userName
			  $Item.LastLogonAD = $dt
			  $Item.LastMailboxLogoff = $AdvStats.LastLogOffTime
			  $Item.LastLoggedOnMailbox = $AdvStats.LastLoggedOnUserAccount
			  $Item.MailboxTotalItemsize = $Advstats.TotalItemSize
			  $Item.MailboxItemCount = $AdvStats.ItemCount
			}
	  	}
	$Collection = $Item.toString()
  }
##########################################################
$DisAcc = Get-Mailbox -database $wdb -resultsize Unlimited | ? {$_.Identity -like "*/Disabled_Accounts/*"}
Foreach ($U in $DisAcc) {Get-AdUserLastLogon $U.SamAccountName}
$Collection | Export-Csv -Path C:\Temp\DisabledAcc_$($wdb).csv
##########################################################
# End
##########################################################

I also tried with select-Object ... | Export-csv -Path ... -append

Answers provided are coming from personal experience, and come with no warranty of success. I as everybody else do make mistakes.