MTN is pushy and *****

Somehow MTN has gotten our office number - which is not listen anywhere - and continues to call to offer me some contract which I have declined at least 3 times. Obviously being a VOIP line and not a cellphone we can't receive any smses so not sure if they think we simply haven't opted out? I have told them multiple times that this is a business and that we are not interested, the last lady that phoned was so rude and argued with me. MTN has no right to ***** our details from wherever nor to continue to call and harass me for a product that I HAVE NO INTEREST IN. Our entire business runs off of a much better service provider. Stop it MTN.