I do pay it, my question qas does their change of contract make it unlawful?

Hello My partner and I took out a secured loan with freedom finance in 2007 for £35,000. We signed the agreement which had our signatures and an agreement number and this document was sent back to Freedom Finance. A few weeks later we got the money through and copies of the documents we had signed. They had crossed out the original agreement number and wrote a new.one in, this wasn't the contract we had signed ...and we didn't intialise the change. Is this contract lawful, can we take this to the County Court to have the agreement overturned? Please advise.