Presuming that OP has quoted the full language of the "refundability" provision, the agent got it wrong and OP is entitled to a full refund of the ticket (it is unused), less $200.
OP may already have a satisfactory solution to the new ticket, but if not, AC may well simply apply the ticket value less $200 to a new ticket on UA/LH routing without a Canadian entry (although if OP selects LH he ought to confirm that he does not require a visa for his FRA transit connection, albeit highly unlikely).
The eTA issue seems to be a red herring as OP's problem appears to be that he is a national of a country for which Canada requires a visa. But, OP might clarify that for us.