Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
I assume you used either control panel software or a command line tool like LEWS to generate your old certificate. Give Certify (which I develop) a try: https://certifytheweb.com - it’s pretty easy to use
Do you remember what client you originally used to generate the certificate on your server? If not, where is your server hosted? Are you able to SSH into your server, or do you use some sort of control panel software to manage your site?
@Sphere, unfortunately this command will only work if the developer installed via apt install certbot, as opposed to via downloading the certbot-auto script. Our users are pretty split between these two installation methods, and our own documentation still suggests each of them to different groups of users.