As part of the spending diary, you need to accuratly account for the costs associated with the taxi work.Leaves you with €2569 for bills food and sundry which doesn't sound bad at all.
Additional insurance, petrol, cleaning etc. etc. etc.
You say €900 to €1000 a week income, when the costs are taken away the take home pay (or profit) might/would be a lot less (unless this is already built into the figure).
The mobile phone bills are very high. Obviously how you deal with this will depend on how tied in you are to the contract. Switching to PAYG (as previously suggested) would reduce this. If you can both stay on one network (Meteor, Vodafone etc.) you might get additional savings for calls to each other (check where the majority of calls are being made... specific networks, landline calls etc. and pick a network to provide the greatest savings for these calls).
Agree with most of the advice above. Your situation isn't really bad (it's one you can get out of given some time and discipline), just hard to see light at the end of the tunnel when you're in the situation.