Disputed invoice

My solicitor received pension sharing forms from the pension company. He initially advised that we didn't need any input from my ex then changed his mind and said it looked like we did. He then spent six weeks trying to get my ex to sign the transfer forms to no avail. We were about to go back to court when my solicitor called the pension company and was told that we didn't need any signature from my ex. I have now received a bill in excess of £900 for this work. It appears to me that I have been misled and if the correct advice had been given at the time then these costs would not have been incurred.

I am going to contact my solicitor and ask who advised him in the beginning.

I've always immediately paid my solicitors bills but this one just seems unfair.

Does anyone have any thoughts.