A few things could be happening here. In your wallet, do you see the address ZTWA.... in the Address History? If so, then you may just be connected to an out-of-sync node. Verify the numbers in the bottom left corner match each other. If they don't, change nodes in Tools -> Edit Node Configuration.
If you do not see the ZTWA address in your address history, try generating a couple of receive addresses to see if the address was at a later "index" from your seed.
If you still do not see the ZTWA address in your history, then you are logging in with the incorrect seed. Double check you are entering your seed correctly. If you copy/pasted it, try typing it. If you typed it, try copy/pasting it. Etc. Sometimes people copy/paste extra characters into the seed box or they typo one or more of the characters.
If that still doesn't work, then you may want to try using this tool that @fvantom
built to help with common mistakes when entering seeds to try and determine what seed you may have used when generating the address for your transfer: https://forum.helloiota.com/7000/Seed-recovery-tool-for-typos
I wish you luck in finding your IOTAs!
Feeling extra generous?
My donation address is: HWY9NVCJISBQLTWMMXOUVYRN9UVRGXWN9RAKZVKMCMUDBQLEVZHM9WZUZCQFELOOBLATONIOPJJ9OIVAXWFUACBGRA