Etihad Airlines - Refund Due

I booked a flight for a colleague on Etihad Airlines around 15 December 2017 from LA to Johannesburg. This was a codeshare flight. When he arrived at the Aer Lingus check-in counter, they had no record of his booking even though we had full tickets in our possession. I had to urgently book him on another flight home with a different airline. Being around Christmas, all flights were fully booked and it was quite a trying time. Since then, I have been in touch with Etihad airlines to get a refund of the R21 160 we paid for the new flight and have been kept waiting because Aer Lingus hadn't come back to them with a reason why my colleague wasn't allowed on the flight. Almost now a year, and I wonder if there is an expiry date for claims and that is why they are hedging with me. Please settle with me so we can end this cycle.