MoMo lack of service . Suspect phishing..

Good day There isn't any way to contact MTN MoMo at all.. I registered a MoMo account on a simcard that got misplaced.I was still using MoMo via the app which I had downloaded a while back.Then i found out recently that someone is using this number.I couldn't do a simswap as I was given the sim by a late friend a few years ago hence I need to change the number registered to my own simcard or at the very least cancel the service .Everywhere I tried gave info to dial 135 which I done on several occasions & was told they couldn't help but was given various apparently direct numbers : *** & *** ...Please try calling them an see for yourselves..One just cuts off continuously and the other goes to a call centre to which you get routed to hold..It never gets answered.I spent several hours on hold on more than a few days...I keep trying them every few days but to no avail at all... I am now suspecting that this is a ********** service & it shocks me to think that a company of MTN's stature would be involved in something so dubious.. If I am unable to resolve this matter , I am turning to consumer watchdogs as well as social media & seeking legal recourse as during the registration process all my details including id number etc were submitted... I would suggest to everyone out there to please keep away from anything MoMo related until clarity is obtained. Thanks