Ben Greenstein didn’t expect to spend more than four hours on the phone over three days just to redeem points for a hotel booking in Boston.

But Mr. Greenstein, an entrepreneur from Baltimore who travels frequently for work, got caught in the not-so-smooth merger in August of Marriott International’s traveler rewards program with the Starwood Preferred Guest and Ritz-Carlton Rewards loyalty programs.

“Prior to this merger, it was never like that,” said Mr. Greenstein, a member of Starwood’s SPG program. When he went online, he said, he found that he was not the only one who couldn’t get help with his account after the merger. “What really bugged me more than anything else was when I went to Facebook and looked on the SPG page and saw how many people were having that problem,” he said.