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.
Just renew your certificate again. I assume the last certificate was included in the recent Let's Encrypt revoke of certificate which use the TLS-ALPN-01 challenge. If you search the forum you will see there was a recent event that required these certificates to be revoked, you should also have received an email from Let's Encrypt about it.
If you are not using TLS-ALPN-01 then you would need to have revoked the certificate yourself somehow.
@itwangxiaobai It would be very helpful if you could answer more questions from the questionnaire. E.g., you probably should know what hosting provider is hosting your website. I.e.: to whom are you paying the bill for your website?