mislaid savings bonds

Hi
I wonder if anyone can help. I've mislaid an old Post OFfice savings bond that was in my own and my sister's name. I contacted the An Post about it today. They now tell me that the bond was cashed two years ago!! They would not tell me if there were one or two signatures on the form used to cash it. Neither of us cashed the bond - we are certain about that. Anyone know how we stand now that we don't have the bond and it would appear that someone forged our name/s.
This is quite distressing as there was about 7,000 euro in this bond.

Would it be the case that the bond had to be sent off for a cheque to issue and then the cheque lodged to another bank account. If so can you chase it up this way.