The Siemens SE587 supports ADSL rather than ADSL2+ per Karoo's latest packages. Every characteristic of your line is suited to ADSL2+.
AFAIK, ADSL2+ should interoperate with your old-speed ADSL equipment. Reset your router to its Factory Defaults and then follow
www.karoo.co.uk/helpandsupport/karoosettings for Karoo Broadband Settings.