Period for erection of a building

In 2016 I was given a building permit by the Municipal Council to start erecting a building on my plot. Because my business was not doing well, I was unable to start the project till January this year. Surprisingly, the Municipal Authority has served me with a letter ordering me to stop the project with immediate effect because 3 years have lapsed before the project took off and I have not sought extension of permit. Is there any legal substance in this letter? Please guide me.
KF, Dar

In view of section 33(1) of the Urban Planning Act, 2007 and regulations 17 and 20 of the Urban Planning (Building) Regulations, 2018, a person given a building permit is supposed to start the project within 6 months of the date of grant of permit and complete the project within 3 years of the grant of permit unless she/he makes an application to the planning authority for extension of time to commence or finish the project. Even with the extension, the aggregate number of days within which the project should be commenced should not exceed 24 months from the date of grant of the permit and should be completed within a maximum of 6 years from the date of grant of the permit.