Can't advise on how to 'recover' your £7.73 (did you pre-pay in some way?) and, in any case, they've not been at the
top of the tree for residential telephony money-saving for some time.
In isolation, there are much cheaper ways to make international calls (I assume you pay your line rental to BT).
1. Check for the cheapest provider for the country you want on
the MSE International Callchecker or on
Niftylist;
2. If all the countries you call are included in the following 28 - Australia, Austria, Belgium, Canada, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Jamaica, Luxembourg, Malta, The Netherlands, New Zealand, Norway, Poland, Portugal, Slovenia, Spain, Sweden, Switzerland or USA - consider signing up for Euphony's £7.25/month
euTalk+12 or £4.33/month
euTalk+18 CPS service.