My mortgage lender said they aren't able to do this and sent a letter saying it's not possible.

Consulting with an estate attorney who understands real estate investment structures can help ensure that your wishes are carried out efficiently.It sounds like you’re on the right track in terms of growing your portfolio, and refinancing into a DSCR loan under your LLC could be a smart move.

We sent old manager a formal letter stating she was not performing so we were hiring new management.

If you use any of the major mailhouse services, like Yellow Letter HQ (a service I can personally vouch for), they offer a variety of templates and even provide text suggestions.A smart way to analyze this strategy is by observing people in your local market who use mailers and identifying what works or doesn’t work for them.The simplest and most effective way to test this approach is to pull a hyper-targeted list of distressed homeowners and run a small-budget mailer campaign.Hope this helps!

If you own your washers and dryers you will probably make some decent money but get ready when something breaks and the tenants want it fixed right away.If you are priced lower than the local laundromat (which most are for some reason) your tenants not only have to carry all their stuff to the Laundromat but will have to spend more money and may want you to cover it.Also a Service Tech will probably charge $100 to show up plus parts. 

Or send them a certified letter?

I got a letter from my mortgage company that said I can move the title into an LLC if I like without triggering the due at sale clause. 

They should be able to send you a pre-approval letter.   

I made and mailed all my yellow letters by hand to cut and save on costs.

Now there can be some exceptions for expensing certain carrying costs, but without knowing specifics it's hard to say at this moment.