If you only have a Telstra phone on plan, then it's unlikely that you're using Telstra Air unless you also have a Telstra home broadband service and modem at home.
Maybe you're actually using free wifi? Some businesses set up their wifi to limit customer's use and to prevent people sitting in cafes all day. Also, it's not very secure for your information or your clients' information.
These connections can also restrict your ability to send and recieve emails with attachments or confidential information in them, which is not practical for business.
However, I'm not sure why you would need internet access to create a document (and an internet drop off would not close the document or erase a saved document).
For a business meeting, you can say you'll get back to them with an answer. If it's important then you'll have to inform them in writing anyway. This delay also gives you time to clarify their request, research options and consequences, get legal or financial advice, and consider if you require anything in return.
Using your mobile as a hotspot would give you a more reliable and private connection, but this may get expensive because you'll be using your mobile data.
Alternatively, you could open a business account. Business accounts get more technical support and plan protections. You might be able to claim costs as work expenses at tax time.
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