http://track-chinapost.com/result_global.php?code=LT311818519CN shows No shipping record. This means your seller never actually shipped anything yet. you might be scammed.

if you just got this number, You should push seller to ship the goods immediately. Tell him if you can not track real shipment data in next 3 days, you will open dispute to aliexpress/amazon/ebay/paypal against fraud.

If you have got this number for long time and paid with paypal/aliexpress, you should open dispute against fraud and claim refund.