Byju's — Frequent unnecessary Calls

Recently I have given my number and Mail id to download a file from their website for study purposes. (To give the number was mandatory to download the file, that's the only reason the number was given) from then onwards they are calling me unnecessarily from their office, asking if I need any service. in the first call itself I noticed that I didn't need any of the services and still, they are sending missed calls, from different numbers, on the same day .. calling again and again disturbing my time and privacy. This has become intolerable.