This is a SCAM! Your messenger service IS enabled and it's easily disabled. Some ass-hat is spamming your messenger service and sending you advertising.
To make it so others cannot send these messages to you, disable the Messenger service from Services. (Go to Control Panel > Perf. & Maint. > Administrative Tools > Services. Double click the Messenger Service, change 'Automatic' to 'Disabled' and click the Stop button.)
Keep your $20 or send it to me