Hidden and Unexplained charges

I received a call from another internet service provider that was offering better rates, I decided being the loyal MWEB customer for over 10 years, I should give them a chance to match it. They managed to offer me a higher package at a slightly discounted rate which I accepted. Was not told of any additional charges. I received a statement of nearly double my normal subscription due to be paid today (01/08/2023). I emailed the retentions department to find out what was going on. The excuse is they charge a pro-rata(which is expected), but this caught me off guard plus ONE month in ADVANCE, since when does a subscriber pay a month in advance but also required to give a month notice which you also pay for when cancelling??? The worst part of all of this is that my package hasn't even been changed over yet. I have paid the pro-rata amount plus their hidden 1 month in advance but still on the old line speed. Does not make any sense to me and seems like daylight *******.