Metro East Mini Storage Of Edwardsville

This storage facility looks nice enough and it is conveniently located; however, I have had frequent problems with them regarding payments. I have mailed them payments and also delivered them myself to their drop-​box at the facility– I’ve had issues both ways.
Twice now, when I’ve dropped the payment off at their drop-​box, they have called me to say that I was late and ask when my payment would be made. When I explained that I dropped the payment off (check sealed in an envelope) in their drop-​box already, I was met with disbelief.
On one occasion they checked the drop-​box THREE times, according to them, and only the last time did they actually (and suddenly!) find my payment in the drop-​box (right were I had left it days earlier! On the other occasion, more recently, they simply said «Nope, we didn’t get it,» after I explained that I personally put it in their drop-​box and I had had a previous problem where it took them three inspections of the drop-​box before the found my payment.
On an occasion when I mailed the payment to them, they called and told me that they had not received it and that I would need to drop it off promptly along with the late fee. I explained that I mailed it weeks earlier and that I was pretty sure that I had seen the check clear my checking account. They assured me that they had not received my payment. I looked up the date that the check cleared and provided them the check number, the bank it was drawn off of, the date it cleared my account and asked them to please take another look at their records. Still, they assured me that they had absolutely no record of the payment.
Finally, I had to get a print out of the front and back of the check (which showed their endorsement stamp on the backside), along with a print out of my bank account showing the check clearing the account and deliver it to them in person before they realized that not only had I made the timely payment, but they had actually deposited the check and it had cleared my account weeks ago!
Such a hassle!
Not to mention the tone they use when they tell you your past-​due (despite really having already paid!)!
UPDATE: Please note that the business did offer to offset my account (via a credit in the amount of) the stop check fee on one occasion. I appreciate that since it was a $ 30 fee.