Can audit service and other service charges invoiced together ?

In future, if you want to ask the tutor directly, please use Ask the Tutor Forums through following link. This forum is primarily designed for students to help one another.

https://opentuition.com/forum/ask-acca-tutor-forums/ask-the-tutor-acca-advanced-audit-and-assurance-aaa-exams/

For your query, i believe there must be separate invoices. If the same firm is providing tax services as well as performing audit, then these are two distinct services and will therefore be invoiced separately.

Regardless of the invoicing, you must know that the same group of people who perform audit cannot offer services like tax or corporate valuation. It gives rise to ethical threat of self-review, as same people who calculated tax figures in financial statements will then be reviewing their own workings.
It is standard practice to use separate teams for the said services, along with signing of confidentiality agreements by the team members.

Hope this helps.