You should be able to call 1850 numbers using your membership/add-on call minutes. See here:
https://48.ie/charges/other-call-charge
If that doesn't work for you then you'll need to contact 48 support and ask them about it. See the link in my signature below.
Alternatively check if there's a regular landline alternative for the 1850 number:
http://www.saynoto1890.com/a-z-listing/
I've never heard of an 1810 number. Are you sure that you meant 1810?
