If you've been emailing and/or leaving voicemails for member services, they are working through a rather large backlog so don't expect a response for 3-4 weeks.
I recommended you call them and keep calling until you actually speak to someone - I find calling first thing in the morning to be a good time.
Or contact them on Twitter - you can see a few people are using this method successfully here:
https://twitter.com/search?f=tweets&vertical=default&q=%40isc2&src=typd
If you need to reinstate your membership, you can login to isc2.org and then go to this form to submit your information: https://www.isc2.org/reinstatement
The Member Support team will contact you to assist with the process. I hope this helps!