This reminded me of an experience from the other side of the argument (although I absolutely know where you're coming from, I've had some terrible experiences with vodafone!!!).
Dh an I are living in Germany and we try our hardest to speak German to people when we go out. We have "mastered" certain phrases that are used a lot and no matter how hard we try and say it perfectly, we suck and it shows on people's faces. Mostly we just get replied to in English which is frustrating in itself because we are trying to learn a second language! It's like they're saying "haha nice try, your German sucks, lets talk English now" (for the record, their English is very good).
Anyway, bit off topic, just thought I'd share