Invalid track number?

Hello,
Sorry, I'm new at your internet-store, so I have some questions again.
On February, 15th I have paid for the goods. Operation code 31W98374W47437152. The same day I have write you the request to add my order to my account. On Feb.,19th you have answered me that my order was dispatched and gave me track No. for it - No.RP404617531SG. More than two weeks passed since my purchase, but I cannot track the parcel yet. All online tracking services say that this tracking No. is unknown.
Could you please check up, may be there is a mistake in tracking number you gave me?
Best regards,