Google "Pattaya visa agent"...
Then scroll down to the map with all locations. There are plenty.
Maneerat Soi 13/2 is often mentioned.
Street back Soi 13 is Thai Visa Service.
Personally I would do it myself
Here is thread if you decide to obtain COR yourself.
https://aseannow.com/topic/1338973-residence-certificate-in-jomtien/