Struggling to pay invoice

My fiancé got a sms this morning regarding a payment that is outstanding for Teljoy. He tried to phone a couple of times, but the line stays busy or he is placed on hold. We also checked his online profile to see there is an invoice that needs to be paid. We tried numerous times now to pay the amount on the invoice, but we have gotten multiple errors on the banking apps and online banking profile. Assistance will be greatly appreciated.