Trying to get my P45 from the job centre but they have said they cant produce copies?

Inland Revenue have taken quite alot of my wage last year in emergency tax, there was a problem when i went from claiming benefits to working. The Inland revenue said i needed to get my P45 from the job centre to prove i am no longer claiming but the job centre have said they sent it out to me and the inland revenue already, yet neither of us have recieved it. This is causing me to be over taxed slightly as well as stopping me from claiming back all the tax they took incorrectly last year.

The inland revenue are saying they cant do anything until they have my P45 and the job centre are saying they cant send a copy. Does anyone have any advise or ideas where i can go from here?

Surly this cant mean i have to stay on the wrong tax code and forget about my tax rebate?