Enrolling in COBRA for second month, no billing statement/forms provided?

I was terminated from my job in August and elected to do COBRA for the month of September (family of 4, lots of Dr appointments). I received paperwork from ADP to elect COBRA mid August and sent in a payment with the signed paperwork to the address provided.

The check was cashed, and I received new insurance cards in the mail (I assumed this meant everything went through), but I never received a billing statement or any other type of confirmation.

I imagined I would get a similar set of paperwork for the month of October, sent in September, to elect to continue coverage for our second month. However, I haven’t gotten anything at all and I’m very concerned about potentially losing coverage if I haven’t sent in payment by October 1st.

I don’t have the paperwork from last time (I had to send in the signed page with the address on it), and I’m not sure who to contact about it. I had ADP as my benefits provider.

Has anyone had this happen to them before? Did I do something wrong? Is there anyone I can reach out to, to get things processed? Is there a way to do this digitally? The mail really makes me nervous.