You could speak with your Landlord in person, however, it is difficult to prove what was discussed.  You could bring a witness, however, that may be uncomfortable for all parties.

You should follow the Landlord Tenant Laws so that your rights are protected.  Instead of CMRRR, you could try next day mail (priority mail) because you would have proof that the package was delivered and who it was delivered to.  Again, though, it is best for you to follow the Landlord Tenant Laws...

If you feel that you were not provided with the proper amount of legally-required notification of the rent increase, send your Landlord a politely written letter that outlines your position and send it to the Landlord by Certified Mail, Return Receipt Requested (keep a copy for your records...) and ask the Landlord for a written response to your concerns within a reasonable time frame (ie. 3 days...).  See how the Landlord responds to your request...