Yes, your solicitor is mistaken. If you want to apply for Ancillary Relief you pay £240.00. If you want to apply for Decree Absolute you pay £45.00. Even if you make the applications at the same time, they are still separate applications.
You can apply for both applications at the same time and pay one fee, for you that would be £285,This sounds very much like the solicitor not understanding your question or you not understanding the answer, so you pay one fee but you pay for each individual application, it would be great if court did BOGOF offers but they don`t.