No communication via email

I made an arrangement with one of the consultants to pay over a 3 month period, i have been asking for the arrangement letter or email from them and have also made the first payment , but they seem to not want to send anything in writing, i have called countless times now and i fail to understand how hard it can be to type out an email or letter stating what was agreed on. My biggest fear is that i will complete payment and wont get any paid up letter.