Cheaper telecom provider...

I've just changed from Telefonica to Ono, being led to believe that I could still keep my previous cheaper supplier for calls to the UK (where I simply prefixed 4 digits before dialling). Now I find that this is not possible. I used to use Fairtel and Elektek prefixes, also Telitec tell me they can't do it, and I can't find contact numbers for the first companies anyway. Ono customer service is practically non- existent, I know they have a scheme where you pay a flat rate per month and then get cheaper calls to UK, however if I'm not out here for 3 months or so in succession, no point in that because any advantages are eaten up by the fixed cost. ANY SUGGESTIONS PLEASE, or am I stuffed into a useless 18-month contract (which includes a very poor and expensive "broadband" service) ?
Hopefully when Ono have pulled their finger out (it's taken months so far) they have promised to port my old number back to me, but I assume that as it would still be on their system, they still have this right to ban other telecoms providers.

I realise that Telitec advertise a UK rate on mobiles around 6 cents a minute to UK, but they add a swingeing connection fee too, so short calls are pricey.

I'd really appreciate any suggestions (that are printable!). Thanks. Steve Riches.