So I left my guild by accident and I was the only member of it. I cant find a way to ask it to customer support so I leave my question here.
Any chance to get back into it? Guild is called Mystries of Live (MOL)
Customer support is here: https://help.guildwars2.com/hc/en-us/requests/new
And yes they are the only ones that may be able to help you in this case.
You need to contact the customer support and tell them what happened. They can restore you to the guild
You may not be able to 're-enter' the Guild, as Guilds are deleted once the last member leaves.
From the Wiki:
If you are the last member to leave a guild then it will be immediately disbanded, deleted and unrecoverable, including all upgrades and anything in the vault. A guild with the same name can be created immediately afterwards.
The CS Team may or may not be able to assist you.
This is exactly why I made a ftp account and invited it to my bank guilds.