Should Lastminute or Delta sort this mess out?

[ohchids]

DS booked a flight to Guatemala. Unfortunately,he put his return date as the 30th of July,instead of August. He had to pay £300 to change the date,but was then informed that he could only stay for 30 days,and was told by Lastminute.com that it was a Delta Airlines policy. Delta are blaming Lastminute. Neither has any 30 day travel limitation in their policies.
DS has now paid £1000 for a 4 week holiday,instead of 7.
Am I being unreasonable to think someone should take responsibility for this mess,when this fact was not disclosed pre booking?
The ideal would be to cancel the ticket,and be refunded,but they won't do this.
I feel that DS has been totally cheated. Can anything be done?

To get this straight, your DS booked the wrong return date for his holiday. He then paid a £300 additional fee to correct it to the right date, but it subsequently transpired that it isn't possible to travel for the length of time his amended booking is for. Is that right? Is it a return flight or two single flights?

If your DS booked with lastminute his contract will be with them - you will have to look at their t's and c's as to whether they are responsible for this. I would think though that if they have allowed a return flight to be booked for a longer period than it is permitted to travel they are in the wrong. I don't really understand the 30 day limit point - is that just a case of your DS needing a visa for longer travel? I don't see how an airline can impose a restriction of this sort otherwise but perhaps a mnetter in the airline industry can educate me on that.