Thank you all!!! Indeed, the seed was incorrect, I found a letter in the mail with a seed that I had entered before and there was another one immediately under it, I tried it and my bitcoins were displayed!
Glad you got it sorted out
For the future, if you want to keep your coins, please move them to a new wallet and do not store your mnemonic code anywhere online (no cloud storage, no email, nothing).
You are risking your coins this way.
The mnemonic code should be stored only offline. Do also not make a screenshot and save it on your hard drive. The best would be to write it down.