The international premium rate telephone number +255 69 978 9506 is being used to make scam wangiri calls to unsuspecting mobile phone owners. If you get a phone call from this number then do not phone back. Anyone who does phone the number +255699789506 will be connected to an expensive premium rate number that will rack up huge charges on your phone bill.
On this occasion the wangiri call appears to originate in Tanzania, because it begins with the international code +255. However international premium rate phone numbers can be purchased from anywhere so there is no guarantee that calls number +255 69 9789 506 were made from that country.