The image is cut off but does it have a City of Boston seal on it? All official communications from city hall will have the city seal on it.

If not this is likely a fake. Also the published 635 number would connect with a city department but it is not publicly listed making it an inside number, possibly as a way to horas someone.

Parking permits usually have assigned serial numbers and that should be also listed on this letter.

Call the main number of the Boston Transportation Department (it's at the city web site) or just call 311 to get connected. Describe the letter and offer the number published.

My initial take is this is a scam.