Were we visited by the MEN IN BLACK? - Strange Agents at our Door!

Kays and dad were just chilling doing their own thing. We were waiting on a call to come in about a close family member who has been ill.

Then there are 3 weird knocks at the door. They were strangely spaced out and very heavy thuds.

Kays answers the door and is greeted by two men dressed from head to foot in black suits, white shirts, black ties, black hats and black shoes.

The two men looked "ill" according to Kayleigh. They were very pale skinned and something seemed off about them.

She asked what they wanted and one of the men said Kayleigh's name, but he kind of comically stuttered pronouncing her surname.

He then passed kays a large brown envelope and they both started walking off.

The envelope had nobody's name or details on it and even though Kays asked the men who it is for, they continued to walk off and did not reply.

We discussed the men and Kays even went back outside, up the alley and looked up and down the road, but did not see them again.

Inside the envelope was a single piece of paper with the following typed words (they looked written on a typewriter):

"DON 'T REVEAL ANY MORE . HEED THE WARNING !"

We think this is probably a prank by someone, but Kays thinks it is a lot of effort to go to for a prank?