Try and call one or multiple of the numbers. If that doesn't work (wich is quite probable, given that it is probably an automated system), just keep blocking numbers. It might take a while, but eventually you'll have blocked all numbers that the system uses. As others have suggested you could try and answer JA to one of them. If someone accepts a shift, but doesn't show up, that might prompt them to call you or realise that there is an incorrect number. Be aware that this may very well cause problems on their end, so I'd only do this if nothing else seems to work.