COMPETENT ASSISTANCE PLEASE!!!

Please make it make sense! I had an account with homechoice in 2011 and I cannot remember what my cellphone number was then. Now someone asked me if they can use my number to check whether they would qualify for a product with you. I then agreed not knowing that I would not be able to use my own number in future if I wished to make use of your services. I then write to customer service, and they advise that I call customer care that told me in the first place I would not be able to utilize any of their services if I do not have that number. Please tell me now, how is it that the system is designed in such a way that it does not leave room for amendments! How do I now look for a number I had 12 years ago! So, I cannot make use of my own number I pay for every month, but I have to go under hypnosis to find that number somewhere in my subconscious! I have mailed them with all the numbers I remember having after looking it up in my gmail and even forwarded my ID and Telkom account bill to proof it's my number!