I queried my high mobile phone bill only to find that there are 5-digit numbers who send SMS messages that cause a charge to be made on your phone bill even though you delete the message un-read. Last month there were 12 such messages and I was charged 22 Euros.
The assistant at Cosmote was helpful and phoned some part of his organisation who has promised to bar all calls from these 5-digit numbers. Apparently, customers of all the mobile providers are victims of this well known theft which, I am told, is illegal but is never prosecuted. The service suppliers know and they continue to accept the charge from these thieves and to pass it on to we innocents.
Do check your bill. Get these thieving numbers barred on your phone.