Certbot and letsencrypt: after renewing my certificate has 2 weeks more of validity instead of 3 months

My letsencrypt certificate will expire soon. I ran "certbot" to renew it for the next 3 months:

  $ sudo certbot certonly --standalone -d $website --email admin@$website
  Saving debug log to /var/log/letsencrypt/letsencrypt.log
  Plugins selected: Authenticator standalone, Installer None
  Cert is due for renewal, auto-renewing...
  Renewing an existing certificate
  Performing the following challenges:
  tls-sni-01 challenge for my_website123.com
  Waiting for verification...
  Cleaning up challenges

  IMPORTANT NOTES:
   - Congratulations! Your certificate and chain have been saved at:
     /etc/letsencrypt/live/my_website123.com/fullchain.pem
     Your key file has been saved at:
     /etc/letsencrypt/live/my_website123.com/privkey.pem
     Your cert will expire on 2018-07-08. To obtain a new or tweaked
     version of this certificate in the future, simply run certbot
     again. To non-interactively renew *all* of your certificates, run
     "certbot renew"
   - If you like Certbot, please consider supporting our work by:

     Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
     Donating to EFF:                    https://eff.org/donate-le

Why "2018-07-08"? I even ran certbot again - the result was the same.

I think you are not renewing the certificate. Just in case, state the certbot version you are using, your linux distribution and your webserver (apache, nginx?)

You can try running with --dry-run the renew command and see the output:

certbot-auto renew --dry-run

Once you check everything is correct, you can run it for real and restart apache:

systemctl stop apache2 &&
certbot-auto renew && 
systemctl start apache2 

If that isn't working (due to certbot version or package), you might need to run the certbot command instead with a pre-hook and post-hook:

certbot renew --pre-hook "service apache2 stop" --post-hook "service apache2 start"

Automate it

Once you solved the issue manually checking for the renewal, you should try to automate it with a cron job, at least weekly if not daily. If you need help with that, leave a comment here and I will update my answer to include it. Most distributions include an automatic renewal with the certbot package.