Edexcel, the largest awarding body for post-16 vocational qualifications, came under pressure from colleges this week to overhaul the weak management that left exam results in chaos this year.
The Association of Colleges has completed a second survey of its members that has exposed flaws in Edexcel's system for dealing with the overwhelming number of queries and complaints about missing and incorrect results for GNVQs and Vocational A levels.
A question mark hangs over the future of Edexcel's chief executive, Tina Townsend, who has yet to return from annual leave. An Edexcel spokeswoman this week declined to comment whether Ms Townsend would return to work.
The survey discovered that problems with Edexcel's service, pointed out by college chiefs in an earlier probe in January, have not been resolved.
They include an inefficient and frequently inaccurate assessment regime and an inadequate call centre system for dealing with subsequent inquiries.
Maggie Scott, the AoC's curriculum and quality advisor, said: "Edexcel tried to deal with the problem by putting more people in the call centre, but... they were not educationalists, and they were not able to transfer callers to people who knew what they were talking about."
An Edexcel spokeswoman added: "We do care and we want to get it right. After what has been a demanding and challenging period, I would ask that we be judged on our performance next year."