The Financial Ombudsman posted a 7.4% rise in complaints it received about financial products between October and December.
The statutory body formed in 2001 to settle disputes between firms and customers, received 41,303 new complaints compared to 38,470 between July and September.
Among residential mortgages, there were 1,732 complaints. A total of 387 of these were referred for a decision from the ombudsman, of which 47% were upheld.
First charge mortgages attracted 1,584 complaints, 333 were handled by the ombudsman and 28% of these were upheld.
Second charge mortgages garnered 121 complaints, 44 were directed to the ombudsman and 35% of these were upheld.
Complaints for Help to Buy mortgages numbered 27, of which 10 went to the ombudsman and 78% of which were upheld, and finally, within this classification, bridging loan complaints numbered fewer than 10.
Meanwhile, in equity release, lifetime mortgages saw 81 complaints, with 46 going to the ombudsman, and 9% being upheld.
Buy-to-let mortgages attracted 202 new complaints, 45 were adjudicated by the ombudsman and 36% of these were upheld.
Overall, the body says that it upheld 38% of the 68,342 new enquiries in the period across the services and products it covers.