faulth phone

Hi, my son bought a Blackberry phone from Carphone Warehouse in May, last week the hole you use to plug charger into went into the phone and so he cannot charge it, he took it back to the shop and after a lot of arguing they said they would get it fixed free of charge (even though he has only had it 4 months) Today i got a message saying they could not repair it and would not exchange it, and the shop are saying it is not their responsibility now. They are trying to blame my son saying that the circuit board has been lifted because the charging part of phone has gone into the phone. They also said in the shop that they have never had this fault reported on this type of phone before. I know my so hasn't caused this damage to the phone but can't make the shop accept that they should be responsible for a faulty phone still under guarantee. Any advice please not sure where to go from here. Thank you
Dawn

Thank you for your reply, my husband went into the shop yesterday as they have got the phone back now. It is now in a worse state than when sent off, the screen is not lined up properly, the shop manager actually pointed this out, and where the charger plugs in is now just a hole. They are showing a picture of the circuit board with damage now how he is suppossed to of done that i do not know. It has been sent off under warranty again for another engineer to look at it. The shop have also sent a report saying that the phone is now in a worse state.
Dawn