Contract Law: Does Agreeing to a Service Make an Invoice Legally Binding

A freight forwarder recently sent me an invoice as I had agreed to move forward with their company to ship my products. Since then, I have emailed them twice in over a week about a question I had regarding the invoice. I have never heard back from them but keep getting "outstanding invoice" emails. Now, we had never agreed to a date for shipment so I am considering a different freight forwarder since I am not hearing back from them. So my question is, am I able to back out of my invoice from the freight forwarder, or does the invoice make it legally binding?

Thanks in advance!

Contract Law: Does Agreeing to a Service Make an Invoice Legally Binding