ERR_CONNECTION_REFUSED is a local configuration / installation problem. That has nothing to to with a CA and with Letsencrypt.
If you want to test something, use the test system. That has it’s own higher limit.
Checking your site the site is online - https://check-your-website.server-daten.de/?q=suffolksp.org.uk#url-checks
Grade I is not good, there are some errors you should fix. But all urls answers, there is no connection refused, creating a screenshot is possible.
And there is a working Letsencrypt certificate:
expires in 73 days suffolksp.org.uk, www.suffolksp.org.uk - 2 entries