Samba also forcefully responded to being called a "negro" on the social network, calling the user who addressed him as "racist" and "small minded".
The 29-year-old arrived to much fanfare in January but in a 3-2 loss at Craven Cottage he showed little of the ability that prompted QPR to fork out a reported £12.5million.
Samba gave away the penalty from which Dimitar Berbatov opened the scoring, before losing possession under pressure to allow the Bulgarian to net his second goal.
"I'm really sorry I let the side down," the defender said through his Twitter account.
"Really upset with my 1st half performance I can't say sorry enough to all the supporters, won't give up."
A little later he added: "Before I go tonight I just want to say I see a lot of you talk about I shouldn't say sorry, well when I'm wrong I'm wrong I hold my hands up.
"Then 2nd of all to all you keep talking about 100k performance, tell me what is a 100k performance? We as players go out and give our all.
"We do are best every week, what I get paid has nothing to do with any of you, as for my price tag I didn't put a price on my head, grow up pls."
After his move from Anzhi Makhachkala to QPR in January, Samba was reported to be picking up a weekly wage of £100,000, but the club have since said the actual sum is lower.