JdmSpec - I would suggest that you phone the provider and outline why you feel that you should not be responsible for the payment of the €165. If they were not providing you with the service thus resulting them being "in breach of service agreement/contract" then you should not be liable for the payment.
The difficulty is in getting hold of the right person - and also how you approach the situation. There is no use in talking to a customer service rep - as they will be bound by limitations - but try to get onto a head of department and explain your case. I dont believe that any reasonable company would make you pay if they were clearly unable to provide a service (by their own admission)
Don't be nasty on your approach - the more reasonable you appear (and have all your facts to hand) the more likely they are to come to a reasonable conclusion. I head up a CS department (thankfully not in telecoms) and frequently come across cases like yours, where people feel that they have not received service etc. I always asses the cases fairly and if the customer is reasonable and has a fair case, I would tend to rule in their favour. Again - there will always be many influencing factors to my decisions, including how the person approaches the situation. It is not worth ruining your credit history for a measly €165, however, It also sounds like you may have a fair justification as to why you should have the amount written off in your favour.