Nothing to worry about, this is perfectly normal. This is the TeleWare service number which is used to route your call. This number will not be presented to the person receiving the call (they will just see the Calling Line Identifier of your Re:Call number).
The cost of this call will depend upon your mobile providers tariffs and will be the same as a call to the London (0207, 0208, 0203 codes). If your SIM provider has a bundle or unlimited package in operation the call will normally come from this allocation. There is no charge to the person receiving the call from your Re:Call App.
