Opodo is jointly owned by a number of European airlines, including BA. They have websites in various European countries but the only one that offers a geographical number for customer service is the Swiss website: +33 1 7300 8900 (strangely enough this is a Paris number).  For bookings this may be OK since the resources are likely to be pooled but for other services for UK customers it may not.

Opodo have 2 addresses in the UK:

......Opodo Limited  ...  registered office is at Waterfront, Hammersmith Embankment, Chancellors Road, London W6 9RU, Great Britain. Please note that all correspondence regarding customer service should be sent to Opodo, PO Box 6589, Leicester, LE1 3ZZ.

Bt directory enquiries returns:

Opodo Ltd
Customer Services
Tel: 0871 277 0090
17 Burley's Way, Leicester, LE1 3BH

Opodo Ltd
General Enquiries
Waterfront
Tel: 0870 352 5000
Hammersmith Embankment Chancellors Road, London, W6 9RU

Searching 192.com for the Leicester address returns:

Hogg Robinson Business Travel International
17 PEGASUS HOUSE
BURLEYS WAY
LEICESTER
Leicestershire
LE1 3BH

Phone:
0116 251 1555

Suggest you try this number and please report back.