HMRC has narrowly missed its call and post handling targets, according to its corporate report on performance for April to September 2014.
During that time the tax department increased the overall number of calls handled to 74.5%, up almost 2% on the same point last year.
But this falls just short of its 80% target.
HMRC says it has received mostly positive feedback from customers regarding the voice recognition service it introduced this year. However, some AccountingWEB members were not so satisfied with the system.
In addition, it said that most callers are now using its cheaper 03 prefix phone numbers. All 0845 numbers will be phased out by December.
Despite the fall in its overall call handling target, the Revenue made improvements in handling tax credits and child benefit calls. Last year, it handled just 16% of calls, but the figure has risen to 89% in 2014. HMRC also said it cleared UK tax credits and child benefit claims and changes of circumstances in an average of 15 days, under its target of 22.
The department trained 2,000 extra staff to help answer phones. But while this has helped them answer more tax credits calls, post handling has suffered.
HMRC cleared 69% of post within 15 working days, down from 77.3% last year. This also falls short of its 80% post handling target.
But it added that the volume of post received continues to drop as it improves its call handling and seeks to resolve queries 'once and done'. It is introducing digital post scanning to improve its performance.
The report added that the Revenue brought in £243.6m in tax this year, £7bn up on 2013. It also secured £8.8bn in additional revenue via its compliance activity and says it is on track to hit its £24.5bn target by year-end.