No message left. Looks like spam call and calling from different numbers, 24003...

Some huge organisation, I suspect, with access to lots of phone numbers.numbers ending (so far) in 23931, 23958, 23959, 23972, 23976, 23983, 24005 and 26332. nobody will leave a message after hearing my recorded message about me not responding to unknown callers who don't leave a legitimate message.

I rang back the number 0488 823 931, spoke with someone who hung up right away

lots of phone numbers beginning with 04888 ending with 23931, 25426, 23967, 23984

I returned a call from 0488 823 931 but the voicemail didn't mention the company name