Lambda Sensor (Engine Management Light) Problem??

Firstly i am new to the site, and wondered if anyone else has experienced this problem before and may also have a solution.

i have a 2004 Model and a few months back the E/M Light came on, i took it to a local garage and they hooked it up to the computer and it showed Lambda sensor bank 1. so they fitted a new front sensor, light went off the next day back on it came so i took it back to the same garage and they then changed the second sensor saying that it might have some how took it out when the first one went, the light went off. the next the the light came back on so i got a friend to look at it for me and he found a broken wire that from the looks of it had been broken a month or so on the front sensor near the floor . but where the wire had broken it was really close to the plug so he looped directly into the wire of the sensor, light went off. the next day the light came back on. so i bought a vw plug from my dealer and he fixed it properly this time but its still on. now it is not running any different than normal, and he is saying that since it was run for a bit and not working properly it might need a cleaning so he did that and light is still on.he now suggests that the sensor might be broke and i might have to get another one.. does anyone have a suggestions for me on this as i have so far spent £250 on nothing and dont want to have to spend even more on something that might not clear this problem..

Thanks