I called back number (03) 7000 5446 reached voice mail but did not say for what company.

I have not answered the phone to this phone number and I've tried to block it several times without success

Switch and save. Telemarketing for energy providers.
Requested number to be remove from list and advised if I receive another call I'll report them to the telecommunications ombudsman.
Caller said he would remove number from their list.