help?

had my linea 24 boiler repaired by vokera 3 weeks ago cost £213. they replaced 9 parts said they would be guaranteed for the year. this week the error code 07 come on so i rang them they said they would come the next day, i waited in for them to come. i got a phone call later on in the afternoon to say they would not becoming because the first repair already came up to £450 and they only repair up to that amount. so they said they would not come out to repair it. the lady on the phone said she had a word with the engineer and he said that error code 7 was a contamination of the system and that it had nothing to do with them as they only mend boilers and would have to get an independent person to clean the system is this right as i dont no were i stand. can any help me?