I don't wish to patronise you, but are you 100% sure that it is Orange's service and not your receiving device that is on the fritz? (Fritz, I haven't used that word in years!)
The answer lies in your contract. Dig out a copy, or use your online account to access it, and there will be a section on the rights and obligations of both parties re services rendered and payments forthcoming. Such contracts are 'standard form' and don't vary from consumer to consumer, so any copy of one (if your friends have one) should do.
For further advice, ring up Orange directly (if you've not done so already). They may be able to explain why the service is intermittent/non-existent or remedies to the issue.
It's doubtful that you can negotiate a reduction in price. The contracts are iron-clad, bar damages clauses for early termination, and the company aren't under any obligation to negotiate with you. (I recognise that they are under an obligation to provide you with a service though!) These types of questions are frequently asked on AB, but there's no loopholes or escape clauses- these large companies aren't stupid (allegedly).
Having read the contractual sections, if you feel you're entitled to treat the contract as voided, contact Orange again and explain why. If all else fails, complain like a demon! That always makes me feel better, even if it's of no great help.