Terrible service after 35 years loyal customer!!!!

On the 13th August 2024 I received a call from MTN informing me that I am due for an upgrade and they wanted to do the upgrade online. I told them that I preferred to do it in person and would visit one of their stores to do so. On the 15th August 2024 my husband and I went to the MTN store in the Kolonade Pretoria where we were assisted and the upgrade was done. My account averages R1700 pm and this month, September, I received a bill in excess of R3000!! I called the 135 number and I was told by a Pamela that the extra R1300 was for an early upgrade!!! Early upgrade!!! My husband and I then went into the store at Kolonade, where I did the upgrade, and they said that the costs were for pro-rata usage and new phone as the billing date is on the 12th and my new contract started on the 15th and thus I had to pay my normal R1700 plus the R1300 for pro-rata usage!!!! I was furious as I said that théy wanted me to upgrade and NOBODY informed me of any pro-rata costs I would be held liable for and had I been told I would have rather waited for the next billing date to avoid said costs. It however appears as if MTN does not care about customers not being given the correct info and costs they might have to pay and they don't advise customers in a way that will protect their customers interest. I have been with MTN since cell phones came out and have NEVER missed a payment or underpaid them. This treatment is unacceptable and I want to advise customers NOT to upgrade at just any date but to make sure that your update will not cause any additional hidden costs. Só dissapointed!!!!!! If this is how MTN treat their loyal customers I cannot imagine what service is given to bad customers!!!!!!!