We paid an extra £80 (£40 each way from Gatwick to Preveza in Greece) to book seats together on our first foreign family holiday. We have two young children who had never flown before. This worked perfectly on our outward journey. However, on the flight back the check in staff had no details of our booking and so gave us different seats - 3 together for my husband and children, and one much further back for me. We had one piece of hand luggage to share between us. We had already paid extra to avoid the family being split up on the flight.
When we returned we complained by email to the online booking agent, who told us to write to another address. I have so far written two letters and had an offer of a £10 refund (with the argument that only my seat booking was not honoured!). The customer service person signs herself 'Emma' and does not give email or phone details. We are having to conduct a postal correpsondence which is getting tedious. I have asked for the name and contact details of her superior but been ignored.