Why wont you send me my monthly invoices

For months now I have been asking why my monthly bills are not being emailed to me. I am still not getting them, i need these for work. I have tried using the MYMTN app to get my bill but it just says there is a problem, try again later. I have tried registering on the web mycontract.mtn.co.za but it wont send me an OTP pin, says my number is a pre-paid which it is not, been a contract phone for close to 15 years. Can someone help me and send me my bill. ***