How can I get an Engineer? ?

Can Anyone identify a VOLKERA engineer who can assist in SHROPSHIRE?
Volkera have only advised (unhelpfully!) that they have no-one who covers a TF postcode
Our local engineer (who installed the boiler) has been unable to repair a fault and advised referring to VOLKERA. Prolonged calls on a o870 number have only elicited the blank described above. Model is LINEA PLUS AG