I don't think you need get field here. Get field allows you to access the contents of a field whose field name is the parameter. Thus, GetField ( tblBills::House )="H" is comparing the contents of the field whose name is stored in tblBills::House to the letter H.
it would be nice to see what the dynamically created URL is, so I might see where I have gone wrong in constructing it
Copy and paste your expression into a Show Custom Dialog script step or a calculation field set to return text.