That seems quite extraordinary. Go back to the firm that set it up, explain the situation and see what they say. Ultimately, if the two of you can't co-operate & go on with it as it stands, then it will have to fail, with whatever consequences are set out in the IVA proposal document (bankruptcy is often stated).
I somehow doubt whether it should have been set up joint. If you can't resolve it & want to complain about the firm that set it up, go to the Insolvency Service site - there is info there about complaining about IPs.