Help Huawei Y300 incoming calls

[Bogart99]

Have a Huawei Y300 that shortly after fitting a sim from Free here in France will no longer accept incoming calls. Outgoing voice and both incoming and outgoing SMS are fine. The symptoms are that if someones tries to call from a landline they get the message "the user is unavailable try later" if calling from a mobile as sooon as the number is dialed the "call ended message" comes upI have tried the sim in a carphone and my wifes phone an ascend also. The problem follows the sim around. I take it I am correct in thinking the
only culprit can be the sim or the operators sytem.

Thanks