MTN does not inform customers that phones are NOT dual sim enabled

Yesterday I received a sms that I can updrade. On logged into my MTN profile to see what upgrades are available. There were three options. I Googled their specifications and decided to go with the Huawei P20 light. Good camera(s), memory, dual sim etc. I went to MTN and said I can upgrade. The lady asked me what phone, I said Huawei P20 light, and the monthly subscription amount so she can see what package it is. I was so excited that they had the blue on in stock! That evening I placed my two sim cards (on MTN as primary, and the other Vodacom for data) in the dual sim card slots. But the phone only detected on sim slot. Nowhere it gave the option for two sim slots. I phoned MTN on 135. The lady said I must swop the two sim cards, because the P20 light is a dual sim (she said). Which I did. But stil it detected only one. I Googled read that MTN lock there second sim slots on all their phones!! I phoned MTN again 135. Again they say the P20 light IS a dual sim, I must go to the shop the next day, and the can't comment on the article I read in Google. First thing the next day I phoned MTN again to speak to another agent. AGAIN I was told the P20 light is dual sim, it's suppose to work, I must go to the shop so they can sort it. I went to the Shop Manager. She asked wether I informed the sales lady that I want a dual sim. And said why must I? Everybody knows the P20 light is dual sim, why must ask/inform them. Why would I even think to do that? My previous phone I got at MTN was (is) dual sim, WHY would I have to mention it. Must I stand there and tell them I want the P20 light because I want dual sim, a 16M camera, 16M selfie, 64G memory, 4G RAM, the specific dimentions, screen resolution, band width, etc? If I want to buy a phone, I do my homework, then go to the shop and say I want this phone. Why must I stand THERE and go through all the specs? According to the manager I did not request wether it's dual sim, and neither does it stand written/advertised that any of the phones at MTN are dual sim. So, I have no excuse. Really? Will I ever have NOT a problem with MTN? O. And the sales lady didn't tell me about the extras for the first month. I only (accidentally) found out today at the MTN shop that I have extras for the first month, which forms part of the contract.