The Isle of Man Steam Packet Company has apologised for call centre problems after ferry sailings over the festive period were cancelled.
Passengers complained on the company's Facebook page they could not get through to its help line after the Ben-my-Chree developed a steering fault.
Chief executive Mark Woodward said "the main issue has been staffing levels" to deal with the extra calls.
The ship is expected to return to the fleet on Wednesday.
Mr Woodward said: "Given the time of year, some staff are away on holiday and this obviously restricted what we could do.
"With it being Christmas, passenger figures for each sailing were high, and this coupled with the limited number of additional staff we could call on meant it was a huge challenge for our team."
He added that, in periods of high call volume, the phone system no longer offers an engaged tone, prompting complaints from some passengers that the phones were "turned off".Phone upgrade
The Ben-my-Chree was scheduled to operate services from Douglas to Heysham and Birkenhead before the engineering fault forced the vessel into dock for repairs.
The company has brought its fastcraft ferry Manannan, which was getting its winter overhaul, back into service for sailings between Douglas and Heysham.
Passengers booked on the original Heysham sailings have been automatically transferred to rescheduled times aboard Manannan.
The company said it would be upgrading the telephone system in the new year.