Some are known to even use fake lawyer letters to send threats.

Quote from @Jason Leigh: Here's what I would do.Write a very short, professional letter to the property manager explaining that they failed to communicate with you about anything, particularly the "services and maintenance" that was never communicated to you or approved by you.

It will include an approval letter from the IRS.

I have many times seen title company balk though and worry about elder abuse etc. and they will want the seller to come in in person and sometimes they will want letter from Sellers attorney saying they agree with the transaction as written etc. 

They will be able to increase their value by $500,000 in 1 month just by sending out a rent raise letter of $10 per unit per month.Do this. 

I borrowed 62k at 10% APR for 12 months with interest only payments and a balloon payment at the end of the loan term.

You can get access for free with a BP Pro plan to try it out. https://inveloapp.com/bigger-pockets/As for straight mail houses, you can check out Open Letter Marketing.

I've gone back and forth between post cards, yellow letters, professional letters, etc. and have been pulled in different directions with different mailing companies. 

You need a pitch to win in a personal letter.

You are terminating their lease, which is done without court involvement.I recommend you present the tenants with an introduction letter as soon as you close on the property.