Consumers have turned to loan providers since last March as lockdowns to fight the COVID-19 pandemic strained their finances.
"For more than a decade, the Financial Ombudsman Service received an unprecedented number of complaints about PPI. We're now seeing thousands more complaints about credit - including about guarantor loans," FOS said in a statement.
Guarantor loans require a friend or family member to guarantee they will take on repayments if the borrower falls behind. Complaints about this type of loan reached more than 10,000 in October to December, up from just over 300 in the same period a year before, the FOS said.
Complaints about other types of home credit jumped to over 6,000 from 430 over the same period.
The complaints about consumer loans usually focused on inadequate affordability checks, FOS said.
Amigo describes itself as Britain's leader in guarantor loans. FOS said complaints about the company totalled 12,854 in the second half of 2020, up from 1,163 in the first half.
Amigo said it launched a scheme of arrangement, or court-approved compensation process, in January after receiving a high number of complaints last year.
"We are a new leadership team that wants to correct past mistakes in a way that is fair and equitable to all our customers - including our 700,000 past borrowers and guarantors," Amigo said in a statement.
Provident Personal Credit Ltd was the second most complained about company, with 10,390 complaints in the second half of 2020, FOS said. Provident had no comment.
PPI became Britain's costliest retail financial scandal that dominated FOS work until the final deadline for complaints passed in August 2019.
(Reporting by Huw Jones; editing by Barbara Lewis)
By Huw Jones
