Calls to 0800 or 0500 numbers are usually free of charge from a UK BT landline. Calls from other providers and mobiles may vary and could cost up to 40p per minute.
Calls to 0845 numbers are typically charged between 1p and 11.5p per minute depending on the time of day for landline customers. They are included free of charge in certain BT call packages. Calls from mobile providers will vary.
Calls to 0345 numbers are the same costs as a call to a standard "01" or "02" landline number, even when calling from a mobile. Calls to an 0345 number are also included in any bundled minutes or free talk time that covers landline calls. Where calls are made outside of a bundle you will be charged at local rate to ring an 0345 number.
The actual cost you are charged will depend on your phone provider. If you are concerned, please contact them to get information about the cost of the call.