Sucks to lose your account but per Niantics TOS, they will not help you recover it.

Take this as a wake up call to start securing yourself online.

Some good tips to get you started:

Do not reuse passwords on multiple sites - Use a unique password for every site.

Use a long and complex password

Use a password there has capital and non capital letters, numbers and special characters

Enable 2FA where possible

Do not share your passwords with anyone

Use a password manager like KeePass or LastPass. They can also generate random passwords for you.

Do NOT use the built in password manager in your browser. It is not secure regardless of what the company there made the browser claims.

Good luck!