Validity of discounted monthly charges on Postpaid Mobile plans

Hi everyone,

I am currently using a prepaid vodafone sim and have never used a postpaid mobil plan before. I noticed there are discounts on monthly cancellable postpaid plans and 5GB extra data per month due to Black Friday. I'm planning to switch to SIM24 porting my current number. (sim24.de Allnet Flat 15 + 5 GB für 6,99 € | monatlich kündbar)

I am assuming the prices will stay the same till the contract is terminated (for monthly cancellable) or for full 24 months for long term contracts. However, on another provider's website (SIMon mobile), it is clearly mentioned that the current rates will change from the 7th month onwards.

I read the product information sheet for sim24 but it doesn't mention anything about price changes after a period. Can anyone clarify if the prices can change after a certain time for sim24 as well?

Thanks for any help!