boleh. If they do not have price freeze agreement when you sign up the account.
But the new package price SHOULD only apply on your next year's hosting. They SHOULD NOT charge extra for your current paid account.
Well, consider moved your site to another webhosting provider if you don't satisfy with that. Moving website to another server is easy.
Shameless selfpromote:
I have 50MB for RM50/year plan too.