You know that you can't turn off multi-currency.   Before you switched it on, you had to check a box that said you understand that you cannot turn it off.   I doubt that customer support has a back-end way to do it but maybe they do.

That being said, it is not terrible. You have all the same functionality as before. You do not lose anything.

" we are unable to create transactions " - that has to be because of something else, not multi-currency.