"got assurance" is correct and usable in written English.
You can use it to express that you received or obtained a sense of security, confidence, or assurance about something. For example: "After asking her boss for an increase in salary, Sarah got assurance that she would be getting paid more in the near future."
He also probably got assurances from Hanoi & Wash.
Nixon travelled to Wheeling only after he got assurances that he would remain on the ticket.
Only after he got assurances from Katz and Robert Iger, president of ABC, did he accept.
But Mr. Riccobono said he got assurances from the chancellor's office that his job was safe.
In recent days, Mr. Obama got assurances from Congressional leaders that most Democrats wanted to do battle and believed that the public was on their side on the issue.
When Lelyveld heard about that sabbatical, he sought — and got — assurances from Arthur that this did not indicate that a decision about the succession had been reached.
"We had a meeting in May last year with Mark Scott and the chairman, Jim Spigelman, and we got assurances of their commitment to religion," Poulos said after the meeting.
"The speaker got assurances that the president would work with him to enact further tort reform in the next Congress," said John Feehery, a spokesman for Mr. Hastert.
"The F.B.I. cannot share information and manage their cases effectively without a top-flight computer system, and we on the commission got assurances again and again from the F.B.I. that they were getting on top of this problem.
They refused to hand over $350 million to $400 million in aid, including Black Hawk helicopters, to military and police forces with a checkered human rights history unless they got assurances that abuses would be prevented and prosecuted.
