Assuming the economy ticket was a pure cash ticket, then I'm afraid it's a "keep calling" every few days until someone understands the question. It's quite clear that agent 1 was clueless, agent 2 not any better, but there are agents at BAEC who have worked there long enough to understand their own scheme. On one call you will eventually get that agent. You will know you are in a better place when that agent gives you an email address beginning ecdocument or this web address:

https://www.britishairways.com/en-gb...ting-documents

You would need to send in your boarding pass and original e-ticket. It's important that the e-ticket shows the booking class, and the layouts do vary between airlines. so it may be the Finnair email tool can help as well. Now normally it doesn't make sense to send off documents without having already spoken to an agent, but one approach is to do this, leave it 24 hours. Then "follow" British Airways on X (formerly Twitter), then direct message them.

Patience is needed, and this is an example where I think you were too quick to PM the BAEC helpers, you haven't got to the end of the road yet.