System Problems and rudeness

I have an agreement on two accounts with the firm, every month I have been paying the instalment via the sms system. Every month I do get the confirmation that the sms was received by the company but there is always an problem that they cannot pick it up as their system doesn't show it, how is this possible ? Every month I get calls of if I did pay or not. I have even began to make more payments so that I can get in advance on the agreement, but apparently their system cannot handle it, according to my records this has been paid now until the end of December 2018. If I do ask for recons you wait for weeks to get it, and then it is still wrong, when you phone the lady is never available and never return your messages that I left. As my situation has not changed yet I can only stick to the current arrangement. I had always had an good relationship with the specific lady but today she just droved me up the wall. Starting with demands and just being purely rude. While I am typing this e mail suddenly smse comes through for a friendly reminder to pay as well as confirmation that they have received the money once again only on one reference number, where is the other one ? I need her to contact me on my cell phone urgently to sort this thing out. I would appreciate if is can ask if I can talk. Waiting on your reply to my e mail.