My ex forged my name to a 401k loan

I would like to know if I am responsible for a loan that my ex took out on his 401k plan through his previous employer. while trying to get the instructions on how to divinde th efunds following our divorce I discovered that my ex had forged my name to a loan document and he is now saying that I have to take less that 50% of the account because since he never repaid the loan( it defaulted) he stopped working at that company so no more payroll deductions were taken out after that time. The loan was to have been paid of by 2005. Now he says that money I get will come out of the net amount ..minus the loan. He also says I will have to claim that amount now as income on my tax return and be responsible for taxes, penalties etc. I thought I was told that the participant is responsible for the loan from the plan administrator when I called her. Now with the forgery issue the company is reluctant to talk to me. Please help.